This study analyzed student test scores to determine if teacher participation in an inquiry-based professional development was able to make a statistically significant difference in student achievement levels. Test scores for objectives that assessed the critical thinking skills and problem-solving strategies modeled in a science inquiry institute were studied. Inquiry-based experiences are the cornerstones for meeting the science standards for scientific literacy. State mandated assessment tests measure the levels of student achievement and are reported as meeting minimum expectations or showing mastery for specific learning objectives. Students test scores from the Texas Assessment of Academic Skills Test (TAAS) for 8th grade science and the Biology End Of Course (EOC) exams were analyzed using ANCOVA, Chi Square, and Logistic Regression, with the Iowa Test of Basic Skills (ITBS) 7th Grade Science Subtest as covariate. It was hypothesized that the students of Inquiry Institute teachers would have higher scale scores and better rates of mastery on the critical thinking objectives than the students of non-Institute teachers. It was also hypothesized that it would be possible to predict student mastery on the objectives that assessed critical thinking and problem solving based on Institute participation. This quasi-experimental study did not show a statistically significant …