Background:
Recent studies on professional development programs indicate these programs, when sustained, have a positive impact on student achievement; however, many of these studies have failed to use longitudinal data. The purpose of this study is to understand the influence of STEM PBL implementation level on students’ achievement after a sustained professional development program.

Material and methods:
Three urban high schools in the southwest U.S. were assigned to participate in a professional development program for STEM teachers. Data for 565 students from these schools were collected at grade 8, 10, and 11. School 1 had a high level of STEM PBL implementation, school 2 showed an average level of STEM PBL implementation, and school 3 had almost no STEM PBL implementation.

Results:
Results from analyses indicated students’ success for school 1 were significantly different than students’ success for schools 2 and 3. Results also indicated no difference in student data for ethnicity in school 1.

Conclusions:
Conclusions drawn from this study suggest full STEM PBL implementation positively influences student achievement whereas partial implementation with another strategy or innovation negatively influences student achievement.