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2 How Teachers Teach: Specific Methods
This chapter discusses several methods of teaching science within the
traditional formats: lectures, discussion sessions, and laboratories. How
can you help your students learn science better and more efficiently in
each format? Although there is no universal best way to teach, experience
shows that some general principles apply (American Association for the Advancement
of Science, 1990a; McDermott et al., 1994; Mazur, 1996):
Evidence from a number of disciplines suggests that oral presentations to large groups of passive students contribute very little to real learning. In physics, standard lectures do not help most students develop conceptual understanding of fundamental processes in electricity and in mechanics (Arons, 1983; McDermott and Shaffer, 1992; McDermott et al., 1994). Similarly, student grades in a large general chemistry lecture course do not correlate with the lecturing skills and experience of the instructor (Birk and Foster, 1993). Enhancing Learning in Large Classes Despite the limitations of traditional lectures, many institutions are forced to offer high-enrollment introductory science courses. Many professors who teach these courses feel that lecturing is their only option, and can only dream of what they could accomplish in smaller classes. However, there is a small but growing group of science faculty members who have developed ways to engage students in the process of thinking, questioning, and problem solving despite the large class size. Strategies in use in introductory courses in biology and geology are described in the sidebars. Although many of the methods described in these sidebars are consistent with what experts know about how students learn (see Chapter 3), they may not be welcomed by all of the students in a class. There are several ways to help students make the transition from passive listeners to active participants in their own learning (Orzechowksi, 1995):
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Biochemistry, Genetics, and Molecular Biology at Stanford University
Professor: Sharon Long
Enrollment: 400 students
One important tool I use to engage students is to create opportunities for
thought and for active pursuit of an unknown during the class session. If
I give a lecture for which I provide notes—a common practice—I always leave
blanks in critical parts of the notes. On the board or transparency, I indicate
the unknown. I pause while I talk about it, drawing the students' attention
to the hole in the notes. If possible, I ask for suggested answers or for
a vote among the possibilities. By arranging the pause in your lecture you
can give the students the chance to puzzle out the question themselves and
to preview their ability to work on the questions independently. And only
by attending class can a student gain all the information—an important draw
to encourage class attendance.
In teaching formal genetics, I draw out a genetic cross first in general form (in this example, a Drosophila eye color inheritance test):
w+y x w w
Then I put into the lecture notes a completely blank Punnett square to show the structure of the approach—but not to provide the answer.
| Female gametes: | |
| Male gametes: |  |
The students encounter this as an unknown, because I address the contents of each line, and each box, as a question. (Everybody, consult with your neighbor for a minute—now second row, anybody tell me, what should be in these two blanks at the top? What would be the genotype and phenotype for the bottom right box?)
Physical Geology at Arizona State University
Professor: Ramon Arrowsmith
Enrollment: 220 students
I show examples of geology from my own experiences, and occasionally include
a few funny slides or video or audio clips to lighten things up. I use a
multimedia presentation system composed of a vertical camera above an illuminated
table on which I write or place rocks, examples from the book, or anything
else I want the students to see. The video signal is projected on a screen
in the classroom. This form of presentation has worked well and definitely
has improved students' access to the material by making things more visible.
Along with the presentation system, I use a laser disc containing movies
and photographs from a textbook publisher. I can easily switch from multimedia
to laser disc output and thus weave visual examples into my lecture. Occasionally,
I show the students computer files or video from a VHS player. The students
react well to this multimedia approach, but to involve the students I have
them do a short exercise in groups, then we talk about it.
For these, I walk up the side of the auditorium and designate even and odd rows. Then I say that the even people should turn around and face the odd people and do the exercise together. This generates groups of 2-6 people. They all put their names onto the single sheet they are to turn in. Then the students work together on a question for 3-4 minutes. I walk around the room, answering their questions.
When time is up, the TA stands at the overhead projector, and I walk through the crowd (I have a lapel mike so they can hear me), collecting their answers for each question. Then we talk about solutions. Usually the time runs out, and the students turn their papers. Of course, they get credit for their participation, and that provides some motivation, but I am sure students understand the concepts better than if they were presented only in my lecture.
This process engages the students. Of course the hub-bub grows as the students move from the assigned topic to other conversations, but they come back fairly quickly. It is a bit unnerving because there is the potential for loss of control in the class, but the students seem to either like it or are indifferent, but certainly aren't quite as passive as they are while being lectured at.
Biochemistry, Genetics, and Molecular Biology at Stanford University Professor: Sharon Long Who doesn't have the experience of having the coiled headset cord
of a telephone show supercoils (twists around itself)? This presents the
students with the chance to play at home, where they can convince themselves
that the direction (handedness) of the supercoils depends on the direction
of the original helix, and on whether the cord was underwound or overwound
before the headset was replaced (constraining the ends). Students learn
both an important principle for understanding nucleic acids and a handy
practical tip that lets them predict the easiest way to get the kinks out
of the phone cord! They get the chance to test their understanding by making
predictions and doing trials—exactly what one hopes for in active scientific
learning. |
A professor's questions should build confidence rather than induce fear. One technique is to encourage the student to propose several different answers to the question. The student can then be encouraged to step outside the answers and begin to develop the skills necessary to assess the answers. Some questions seek facts and simply measure student recall; others demand higher reasoning skills such as elaborating on or explaining a concept, comparing and contrasting several possibilities, speculating about an outcome, and speculating about cause and effect. The type of question asked and the response given to students' initial answers are crucial to the types of reasoning processes the students are encouraged to use. Several aspects of questions—to formulate them, what reasoning or knowledge is tested or encouraged, how to deal with answers—similar for dialogue and for testing. Chapters 5 and 6 contain more information on questions as part of assessment, testing, and grading.
Demonstrations can be very effective for illustrating concepts in class, but can result in passive learning without careful attention to engaging students. They can provoke students to think for themselves and are especially helpful if the demonstration has a surprise, challenges an assumption, or illustrates an otherwise abstract concept or mechanism. Demonstrations that use everyday objects are especially effective and require little preparation on the part of faculty (see sidebar). Students' interest is peaked if they are asked to make predictions and vote on the most probable outcome. There are numerous resources available to help faculty design and conduct demonstrations. Many science education periodicals contain one or more demonstrations in each issue. The "Tested Demonstrations" column in the Journal of Chemical Education and the "Favorite Demonstration" column in the Journal of College Science Teaching are but two of the many examples. The American Chemical Society and the University of Wisconsin Press have published excellent books on chemical demonstrations (Shakhashiri, 1983, 1985, 1989, 1992; Summerlin and Ealy, 1985; Summerlin et al., 1987). Similar volumes of physics demonstrations have been published by the American Association of Physics Teachers (Freier and Anderson, 1981; Berry, 1987). |
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You should consider a number of issues when planning a demonstration
(O'Brien, 1990):
Small group discussion sections often are used in large-enrollment courses to complement the lectures. In courses with small enrollments, they can substitute for the lecture, or both lecture and discussion formats can be used in the same class period. The main distinction between lecture and discussion is the level of student participation that is expected, and a whole continuum exists. Discussions can be instructor-centered (students answer the instructor's questions) or student-centered (students address one another, and the instructor mainly guides the discussion toward important points). In any case, discussion sessions are more productive when students are expected to prepare in advance.
Focused discussion is an effective way for many students to develop their conceptual frameworks and to learn problem-solving skills as they try out their own ideas on other students and the instructor. The give and take of technical discussion also sharpens critical and quantitative thinking skills. Classes in which students must participate in discussion force them to go beyond merely plugging numbers into formulas or memorizing terms. They must learn to explain in their own words what they are thinking and doing. Students are more motivated to prepare for a class in which they are expected to participate actively. However, student-centered discussions are less predictable than instructor-centered presentations, they are more time consuming, and they can require more skill from the teacher. To lead an effective discussion, the teacher must be a good facilitator, by ensuring that key points are covered and monitoring the group dynamics. Guidance is needed to keep the discussion from becoming disorganized or irrelevant. Some students do not like or may not function effectively in a class where much of the time is devoted to student discussion. Some may take the point of view that they have paid to hear the expert (the teacher). For them, and for all students, it is useful to review the benefits of discussion-based formats in contrast with lectures whose purpose is to transmit information. Sensitivity to personality, cultural, linguistic, and gender differences that may affect students' participation in discussions is also important, especially if participation is graded. When students do not spontaneously engage in a discussion, they may be unprepared or they may be reluctant to speak or to be assertive. Some may be more comfortable making comparisons than absolute statements, and others may be more comfortable with narrative descriptions than with quantitative analysis. You might try various strategies to engage your students in meaningful discussion by posing questions that measure different levels of understanding (knowledge, application, analysis, and comprehension; see Chapter 6).
Planning and Guiding Discussions Probably the best overall advice is to be bold but flexible and willing
to adjust your strategies to fit the character of your class. If you want
to experiment with using discussions in your class, here are some things
to consider:
Collaborative learning "is an umbrella term for a variety of educational
approaches involving joint intellectual effort by students, or students
and teachers together" (Goodsell et al., 1992). Cooperative learning,
a form of collaborative learning, is an instructional technique in which
students work in groups to achieve a common goal, to which they each contribute
in individually accountable ways (Stover et al., 1993). The interaction
itself can take different forms:
Although cooperative learning has been used effectively in elementary, middle, and high schools for a number of years, as discussed by Johnson and Johnson (1989) and Slavin (1989), few studies have been done to demonstrate its effectiveness in the college classroom. Nevertheless, a growing number of practitioners are assessing its effectiveness (Treisman and Fullilove, 1990; Johnson et al., 1991; Smith et al., 1991; Caprio, 1993; Posner and Markstein, 1994; Cooper, 1995; Watson and Marshall, 1995). While many advocates of collaborative learning are quick to point out its advantages, they are also sensitive to its perceived problems. Cooper (1995), for example, points out that coverage, lack of control during class, and students who do not carry their weight in a group, need to be considered before embarking on collaborative learning. In addition, the evaluation of group work requires careful consideration (see Chapter 6).
It is hard to imagine learning to do science, or learning about science, without doing laboratory or field work. Experimentation underlies all scientific knowledge and understanding. Laboratories are wonderful settings for teaching and learning science. They provide students with opportunities to think about, discuss, and solve real problems. Developing and teaching an effective laboratory requires as much skill, creativity, and hard work as proposing and executing a first-rate research project. Despite the importance of experimentation in science, introductory labs fail to convey the excitement of discovery to the majority of our students. They generally give introductory science labs low marks, often describing them as boring or a waste of time. What is wrong? It is clear that many introductory laboratory programs are suffering from neglect. Typically, students work their way through a list of step-by-step instructions, trying to reproduce expected results and wondering how to get the right answer. While this approach has little do with science, it is common practice because it is efficient. Laboratories are costly and time consuming, and predictable, "cookbook" labs allow departments to offer their lab courses to large numbers of students.
Developing Effective Laboratories Improving undergraduate laboratory instruction has become a priority in many institutions, driven, in part, by the exciting program being developed at a wide range of institutions. Some labs encourage critical and quantitative thinking, some emphasize demonstration of principles or development of lab techniques, and some help students deepen their understanding of fundamental concepts (Hake, 1992). Where possible, the lab should be coincident with the lecture or discussion. Before you begin to develop a laboratory program, it is important to think about its goals. Here are a number of possibilities:
Developing an effective laboratory requires appropriate space and equipment and extraordinary effort from the department's most creative teachers. Still, those who have invested in innovative introductory laboratory programs report very encouraging results: better understanding of the material, much more positive student attitudes toward the lab, and more faculty participation in the lab (Wilson, 1994). Many science departments have implemented innovative laboratory programs in their introductory courses. We encourage you to consult the organizations and publications listed in the Appendices. Education sessions at professional society meetings are another opportunity to get good ideas for labs in your discipline. Some faculty members have given up lecturing and large class meetings in favor of supervised collaborative learning in laboratory settings. Such workshop methods have been devised for teaching physics (Laws, 1991), chemistry (Lisensky et al., 1994), and mathematics (Baxter-Hastings, 1995). Although this is not feasible at many institutions, some of the ideas developed in these courses translate reasonably well to courses in which a lab is associated with a large-enrollment course (Thornton, in press). |
Animal Behavior Laboratory at Princeton University
Professor: James L. Gould
Enrollment: approximately 50 students in 3 sections
A major goal of this course is to teach students how to do science: collect
initial observations, formulate testable hypotheses, perform tests, refine
or overhaul the original hypothesis, devise a new test, and so on. Each lab
is two weeks long, with the equipment and animals available for the entire
time. All of the materials that students could plausibly need are stored
on shelves for easy and immediate access. In the first hour, we discuss
the lab and possible hypotheses, and look over the materials at hand. Each
group then formulates an initial plan, obtains approval for their plan,
and conducts the experiment.
The most flexible labs utilize computer-controlled stimuli. In one lab, students are asked to determine to what features of prey a toad responds. Although they begin with live crickets and worms, they are encouraged to use a computer library of "virtual" crickets and toads. Students are given instructions for making new prey models, or modifying existing ones, to test the toad's response to different features. The library includes variations of shape, motion, color, three-dimensionality, size, and so on, plus a variety of cricket chirps and other calls. In general, students quickly discover that virtual crickets work almost as well as real ones—better in that they provide more data since the toad never fills up! A simple statistical program on the computers helps minimize the drudgery of data analysis, enabling the students to concentrate on experimental design and results rather than tedious computations.
A number of other labs in the course make use of computer-generated
and modified stimuli. Labs using this strategy deal with mate recognition
in crickets and fish, competitor recognition in fish, predator recognition
in chicks and fish, imprinting in ducklings, color change in lizards, and
hemispheric dominance in humans.
Cooperative Learning in the Laboratory
Students in two laboratory sections of a chemistry course for non-science majors worked in groups of three on two experiments about acids, bases, and buffers. The experiments were devised using a modified "jigsaw" technique, in which each student in a group is assigned a particular part of a lesson or unit and is responsible for helping the other members of the group learn that material. The week prior to the laboratory, students were given lists of objectives and preparatory work that were divided into three parts. Students decided how to divide the responsibility for the preparatory and laboratory tasks, but were informed that the scores from their post-laboratory exams would be averaged, and that all members of a group would receive the same grade. Two control sections of the same laboratory were conducted in a traditional manner, with students working independently.
All four groups of students were part of the same lecture class, and there were no significant differences in age, gender balance, or previous number of chemistry classes. Although the control sections had an overall GPA higher than the cooperative learning sections (2.77 versus 2.30), the students in the cooperative sections had higher overall scores on the post-lab tests. The authors conclude that use of cooperative learning in the laboratory has a positive effect on student achievement.
Smith et al., 1991.
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Laboratories can be enriched by computers that make data acquisition and analysis easier and much faster, thus allowing students to think about their results and do an improved experiment. Computers can also be used as an element of the experiment to simulate a response, or vary a stimulus. Computers offer convenience, flexibility and safety in the laboratory, but they should not completely replace the student's interaction with the natural world. Laboratory teaching methods vary widely, but there is certainly no substitute for an instructor circulating among the students, answering and asking questions, pointing out subtle details or possible applications, and generally guiding students' learning. Although students work informally in pairs or groups in many labs, some faculty have formally introduced cooperative learning into their labs (see sidebar). Some instructors rely on a lab handout, not to give cookbook instructions, but to pose a carefully constructed sequence of questions to help students design experiments which illustrate important concepts (Hake, 1992). One advantage of the well-designed handout is that the designer more closely controls what students do in the lab (Moog and Farrell, 1996). The challenge is to design it so that students must think and be creative. In more unstructured labs the challenge is to prevent students from getting stranded and discouraged. Easy access to a faculty member or teaching assistant is essential in this type of lab. Once you have decided on the goals for your laboratory, and are familiar with some of the innovative ideas in your field, you are ready to ask yourself the following questions:
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Helping Teaching Assistants to Teach in the Laboratory |
The various methods by which students report their lab work have different pedagogical objectives. The formal written report teaches students how to communicate their work in journal style, but students sometimes sacrifice content for appearance. Keeping a lab notebook, which is graded, teaches the student to keep a record while doing an experiment, but it may not develop good writing and presentation skills. Oral reports motivate students to understand their work well enough to explain it to others, but this takes time and does not give students practice in writing. Oral reports can also motivate students to keep a good notebook, especially if they can consult it during their presentation. In choosing this important aspect of the students' lab experience, consider how your students might report their work in the future.
Teaching Labs with Teaching Assistants Many benefits of carefully planned laboratory exercises are realized only if the instructional staff is well prepared to teach. Often the primary, or only, lab instruction comes from graduate or undergraduate teaching assistants or from faculty members who were not involved in designing the lab. Time must be invested in training the teaching staff, focusing first on their mastery of the lab experiments and then on the method of instruction. It is a fine art to guide students without either simply giving the answer or seeming to be obstinately obscure. Teaching assistants who were not taught in this way can have difficulty adapting to innovative laboratory programs, and the suggestions below will you help you guide their transition. A good part of the success of a course depends on the group spirit of the whole team of instructor and teaching assistants. Many such groups meet weekly, perhaps in an informal but structured way, so that the teaching assistants can provide feedback to the instructor as well as learn about the most effective way to teach the next laboratory experiment (see sidebar). |
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The responsibility for preparing teaching assistants is largely dependent on the setting. While many faculty members at four-year institutions are responsible for preparing their teaching assistants, this task is handled on a department-wide or campus-wide basis in programs with large numbers of graduate students. Many professional societies have publications on this topic (see Appendix A). The American Association for Higher Education is another excellent source of information. Their publication Preparing Graduate Students to Teach (Lambert and Tice, 1993) provides numerous examples of teaching assistant training programs in a wide array of disciplines. |
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