To support implementation of the "Next Generation Science Standards," we designed a high school biology unit, "Matter and Energy for Growth and Activity" (MEGA), that engages students in explaining physical and life science phenomena using evidence, models, and science ideas about matter and energy changes within systems and transfers between systems. The unit's promise was evaluated using a randomized control trial (RCT) involving fifteen teachers from two schools. Teachers were randomly assigned to implement either the MEGA unit or district-developed activities that targeted the same learning goals. Pre- and post-tests were administered, and the data were analyzed using Rasch modeling and hierarchical linear modeling. Here we describe the unit and report on RCT results. Our data showed that, when controlling for pretest score, gender, language, and ethnicity, students in the treatment group performed better on the post-test than the students in the comparison group, indicating the MEGA unit has promise in improving students' understanding. We also discuss a number of challenges that arose when developing and evaluating the unit.