Child Trends describes a pair of evaluation studies, a baseline and a follow-up from a year later:
Bierman, K. M., Domitrovich, C. E., Nix, R. L., Gest, S. D., Welsh, J. A., Greenberg, M. T., Blair, C., Nelson, K. E., & Gill, S. (2008). Promoting academic and social-emotional school readiness: The Head Start REDI program. Child Development, 79(6), 1802-1817.
“Results: In the spring of the school year, children participating in Head Start REDI classrooms were found to have significantly better outcomes, compared with the control group, in several domains, including vocabulary (effect size = .15), emergent literacy skills (effect sizes ranging from .35 to .39, depending on measure), social-emotional awareness and responses (effect sizes ranging from .21 to .35, depending on measure), teacher-reported aggression (effect size = -.28), learning engagement at school (effect size = .29), and learning engagement at home (effect size = .25).” Retrieved from https://web.archive.org/web/20170705050709/https://www.childtrends.org/programs/the-head-start-redi-program/
Bierman, K. M., Nix, R. L., Heinrichs, B. S., Domitrovich, C. E., Gest, S. D., Welsh, J. A., & Gill, S. (2008). Effects of Head Start REDI on children’s outcomes 1 year later in different kindergarten contexts. Child Development, 85(1), 140-159.
“Results: No significant group differences were found on teacher-child interaction quality, emphasis on reading instruction, or school-level student achievement. Compared with the original control group, children who had been in Head Start REDI classrooms at age four were found to have significantly better outcomes toward the end of their kindergarten year (one year post-intervention) on one measure of emergent literacy skills (effect size = .25), learning behaviors (effect size = .28), competent problem solving (effect size = .40), teacher-rated aggression (effect size = -.26), and parent-rated aggression (effect size = -.22).” Retrieved from https://web.archive.org/web/20170705050709/https://www.childtrends.org/programs/the-head-start-redi-program/