Having recently shared some of the most promising recent RCT findings, I now share one of the most disconcerting: The long-term results of the Tennessee voluntary Pre-K study. Quick take: High-quality RCT finds adverse effects on student achievement and behavior in 6th-grade follow-up.

Program:

• Tennessee’s voluntary Pre-K (VPK) program is a statewide program for 4-year-old children from low-income families. In 2009-10, when the treatment group received VPK, the program met 9 of 10 quality benchmarks of the respected National Institute for Early Education Research (link, p. 133).

Study Design:

• The study randomly assigned 3,131 children, via lottery, to VPK vs control. The authors published results of a 6th-grade follow-up. Based on careful review, I believe this was a high-quality RCT (e.g., with low attrition and good baseline equivalence)

Findings at 6th Grade:

• The study found statistically significant adverse effects on English language arts, math, and science on the state test. Effect sizes were about -0.15, meaning VPK would've moved the average control group child from the 50th to 44th percentile had he or she been assigned to the VPK group.

• Also: modest adverse effects on % of special ed placements (12% VPK vs 8% control) and disciplinary events in grades K-6 (effect size 0.09) - both statistically significant.

Comment:

• It's unclear what accounts for VPK's adverse effects. Study author Dale Farran offers some ideas.

• Both this study and the national Head Start RCT found positive effects at end of Pre-K that dissipated as kids entered grade school. But in VPK (unlike Head Start) the impacts turned negative.

• The findings underscore why it's essential for government funding of Pre-K to incorporate evidence-based criteria aimed at ensuring effectiveness - e.g., RCTs to identify truly effective practices (curricula, teacher training, etc.), and funding to implement these practices - as discussed here.