In recent years, science educators have struggled with the dual challenge of equity and excellence, of providing all students access to a quality science education, and ensuring each student achieves an understanding of scientific concepts and processes. The Program for Complex Instruction, a model of group work, addresses this dual challenge by teaching various subject matter at a high intellectual level to students with diverse academic skills. By examining science learning in Complex Instruction classrooms, insight into the following three questions was sought: (1) What scientific facts, concepts, and applications do students learn during group work?; (2) Are all students provided equal access to science learning?; and (3) What are the strengths and limitations of using open-ended paper-and-pencil tests to measure student learning of science? The study was conducted in 13 middle school science classrooms over the course of 2 years. The results are organized into four areas of interest: conditions for learning, excellence, equity, and issues of test construction. Findings include: all observed classrooms met the standard for the percentage of students talking and working together; significant gains were found on all five pre-, post-tests concerning the topics of systems, respiration, digestion, circulation; reading scores were significantly correlated with the pre- and post-test scores on each of the five unit tests; gender effects were found on the various tests but they varied by grade level; and on some tests (respiration and circulation 2) students scored higher when tests lacked large percentages of drawings or diagrams while other tests (digestion and circulation 1) showed gains when large amounts of diagrams were included. Contains 19 references. (MVL)