This study examined the impact of a multi-year, large-scale professional development program on student achievement in mathematics and science. Math and science teachers at the elementary and secondary levels who participated in the professional development program were matched to a control group. Results revealed no differences in State of Texas Assessments of Academic Readiness (STAAR) test scores between treatment and control groups for all grades and subjects except elementary students in rural areas. In rural areas, fifth grade students of teachers in the treatment group outperformed students of teachers in the control group on the STAAR Math and STAAR Science assessments. These results suggest that the large-scale professional development program is particularly beneficial for rural elementary school teachers, perhaps due to rural teachers having a greater need for the connections and resources gained by participating in the program and to elementary teachers having more flexibility in the amount of time they spend teaching math and science in their classrooms.