The purpose of this cross-sectional study was to investigate the effects of a multi-year implementation of the Science IDEAS model on (a) the Iowa Tests of Basic Skills (ITBS) achievement growth in Reading Comprehension and Science of grade 3-5 students receiving the model, and (b) the transfer effects of the model as measured by ITBS Reading Comprehension and Science to grades 6-8. In doing so, a major objective of the study was to demonstrate the implications for school reform of increasing the instructional time for in-depth science instruction as a means for accelerating student achievement in both reading and science. The study was conducted in a large (185,000 students), diverse (African American: 29%, Hispanic: 19%, Other: 5%, Free Lunch: 40%) urban school system in southeastern Florida. The findings of this multi-year, cross-sectional study substantially extend previously reported research demonstrating the effectiveness of content-area learning in science as a means for improving student reading comprehension. In doing so, this study is suggestive of reversing current curricular policy that emphasizes the major allocation of student instructional time to non-content-oriented basal reading programs in place of meaningful content-area instruction. Implications of the present study are that a curricular approach integrating literacy within in-depth science instruction potentially has the dual benefit of directly and, on a transfer basis, increasing student academic achievement in these two critical areas. (Contains 2 tables and 2 figures.)