This article reports the results of a randomized control trial of a semester-long intervention designed to promote ninth-grade science students' use of text-based investigation to create explanatory models of biological phenomena. The main research question was whether the student participants in the intervention outperformed the students in the control classes, as assessed by several measures of comprehension and application of information to modeling biological phenomena not covered in the instruction. A second research question examined the impact on the instructional practices of the teachers who implemented the intervention. Multilevel modeling of outcome measures, controlling for preexisting differences at individual and school levels, indicated significant effects on the intervention students and teachers relative to the controls. Implications for classroom instruction and teacher professional development are discussed.