build upon each other within and across content areas are other important aspects of the depth of understanding. The depth of understanding of science content required varies according to the grade level of teaching responsibility.

Teachers of grades K-4 usually are generalists who teach most, if not all, school subjects. A primary task for these teachers is to lay the experiential, conceptual, and attitudinal foundation for future learning in science by guiding students through a range of inquiry activities. To achieve this, elementary teachers of science need to have the opportunity to develop a broad knowledge of science content in addition to some in-depth experiences in at least one science subject. Such in-depth experiences will allow teachers to develop an understanding of inquiry and the structure and production

of science knowledge. That knowledge prepares teachers to guide student inquiries, appraise current student understanding, and further students' understanding of scientific ideas. Although thorough science knowledge in many areas would enhance the work of an elementary teacher, it is more realistic to expect a generalist's knowledge.

Science curricula are organized in many different ways in the middle grades. Science experiences go into greater depth, are more quantitative, require more sophisticated reasoning skills, and use more sophisticated apparatus and technology. These requirements of the science courses change the character of the conceptual background required of middle level teachers of science. While maintaining a breadth of science knowledge, they need to develop greater depth of understanding than their colleagues teaching grades K-4. An intensive, thorough study of at least one scientific discipline will help them meet the demands of their teaching and gain appreciation for how scientific knowledge is produced and how disciplines are structured.

At the secondary level, effective teachers of science possess broad knowledge of all disciplines and a deep understanding of the scientific disciplines they teach. This implies being familiar enough with a science discipline to take part in research activities within that discipline.

Teachers must possess the skills necessary to guide inquiries based on students' questions. An important test of the appropriate level of understanding for all teachers of science at all levels is the teacher's ability to determine what students understand about science and to use this data to formulate activities that aid the development of sound scientific ideas by their students.

Prospective and practicing teachers of science acquire much of their formal science knowledge through coursework in colleges and universities. For all teachers, undergraduate science courses are a major factor in defining what science content is learned. Those courses also provide models for how science should be taught. For K-4 teachers