Student's performance in science classrooms has continued to languish throughout the USA. Even though proficiency rates on national tests such as National Assessment of Educational Progress are higher for Caucasian students than African-Americans and Hispanics, all groups lack achieving desired proficiency rates. Further, the Next Generation Science Standards detail a new higher benchmark for all students. This study analyzes a professional development (PD) project, entitled Inquiry in Motion, designed to (a) facilitate teacher transformation toward greater quantity and quality of inquiry-based instruction, (b) improve student achievement in science practices and science concepts, and (c) begin to narrow the achievement gap among various groups. This 5-year PD study included 11 schools, 74 middle school teachers, and 9,981 students from diverse, high minority populations. Findings from the quasi-experimental study show statistically significant gains for all student groups (aggregate, males, females, Caucasians, African-Americans, and Hispanics) on all three science Measure of Academic Progress tests (composite, science practices, and science concepts) when compared to students of non-participating teachers. In addition to an increase in overall performance for all groups, a narrowing of the achievement gap of minority students relative to Caucasian students was seen. When combined with other studies, this study affirms that, when facilitated effectively, inquiry-based instruction may benefit all students, for all demographic groups measured.