instructional approaches in upper-division courses, although some has been conducted (see, for example, Chasteen and Pollack  and Smith et al. ). Within introductory courses it is unclear whether student-centered learning environments affect different student populations differently, because DBER scholars rarely compare the effects of a given strategy for different student populations. Populations of interest for future study include students who are underrepresented in science, including students for whom English is a second language, females, and ethnic/racial minorities. It also would be useful to explore the dimensions of overall science performance, quantitative skills, and spatial ability. Further study is needed on strategies to accommodate students with disabilities into the full suite of instructional opportunities, especially laboratory and field-based learning.
Across the disciplines in this study, the role of the laboratory class is poorly understood. It would be helpful for scientists, engineers, and DBER scholars to identify the most important outcomes of a well-designed laboratory course, then to design instruction specifically targeted at those outcomes and instruments for routinely assessing those outcomes. Future DBER might compare learning outcomes associated with different types of laboratory instruction (e.g., free-standing versus laboratory activities that are integrated into the main course) and compare outcomes in courses where laboratories are required, optional, or not offered. In addition, laboratory activities in which students conduct inquiry on large, professionally collected data sets (such as genomics data and geoscience datasets served by the U.S. Geological Survey, the National Oceanic and Atmospheric Administration, the National Aeronautics and Space Administration, and various university consortia) have grown in prominence in recent years (Hays et al., 2000), but have been little studied.
Additional research also is needed on field-based learning. Specifically, which types of field activities promote different kinds of learning and which teaching methods are most effective for different audiences, settings, expected learning outcomes, or types of field experiences? The research base is particularly sparse regarding the degree of scaffolding needed for different types of field activities, and which types of field projects are optimal for a given learning goal (Butler, 2008). Given the expense and logistical challenges of field-based instruction, it is important to identify which learning goals (if any) can only be achieved through field-based learning, and which (if any) could be achieved through laboratory or computer-based alternatives. These studies also should explore affective dimensions of field learning, including motivations to learn science and cultural and other barriers to learning.
In studying the efficacy of different instructional approaches, DBER scholars must take into account the time constraints of instructors. Future DBER studies might document the time associated with different