Professional Development as a school intervention is validated by the work of Timperley, Wilson, Barrar, and Fung (2007) who found 72 studies that assessed the effects of professional development on student outcomes. Based on their meta-analysis of these studies, the overall effect on student outcomes was d = .66, validating that professional development has a significantly significant effect on student outcomes which is significantly higher than the minimal standards of the WWC’s (d = .25).