With only 34% of 8th grade students earning a rating of proficient or higher in science education (from the 2011 National Assessment of Education Progress data), much work is needed in our classrooms to achieve the new more rigorous performance expectations found in the "Next Generation Science Standards." For decades, researchers have espoused the importance of constructivist-based methods such as inquiry-based instruction to meet the more rigorous performance expectations found in K-12 science education. However, current research is sparse relative to linking the effect of long-term interventions to the academic growth of students in science. This six-year study, involving 219 teachers and 15,292 students, sought to link the involvement of teachers in a sustained professional development intervention to student academic growth. Specifically, the intervention was designed to improve the quantity and quality of guided inquiry-based instruction in middle school science classrooms. Using a quasi-experimental design, we sought to measure if the growth scores of students of teacher participants exceeded the scores of students of non-participating teachers and students from a similarly matched virtual comparison group (VCG) on the MAP (Measures of Academic Progress) science test. Medium to high effect sizes were noted for growth scores of students of participating teachers above what was expected for the VCG. Specifically, students of teachers who participated in the intervention consistently exceeded the growth expectations by 29-82% (depending on the test and the number of years of involvement in the intervention). This study supports prior research findings that inquiry-based instruction helps improve students' achievement relative to scientific practices, but this study also shows that improved conceptual knowledge is a byproduct of effective inquiry-based instruction. Further research is needed to see if these findings hold for all grade levels.