The purposes of the Colorado Science Teaching Enhancement Program (CO-STEP) are to improve the background in science content and the instructional skills of teachers in grades four through six throughout Colorado and to support the implementation of effective instruction. A network of six Teacher Development Centers in Colorado coordinate teacher enhancement programs and follow-up implementation support. Physical science (physics, chemistry, geology, meteorology, and astronomy), life science, and environmental science content that is essential to teaching science in the upper-elementary grades is a central focus of the program. Teachers also learn how to infuse the science content into their curriculum and instruction. During the program teachers develop instructional skills, including cooperative learning, constructivist-based teaching strategies, and innovative assessment procedures. Participating teachers adapt instructional units from existing curriculum materials and field test, evaluate, and revise the units for use in their classrooms. This document discusses the project goals and objectives, project design, rationale for CO-STEP, general model of the teacher development program, the teacher development program, evaluation plan, evaluation results (quantitative and qualitative) for each of the centers, and conclusions. Contains 67 references. (LZ)