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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 & behavior in 6th-grade follow-up.


  • 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 & good baseline equivalence)

Findings at 6th Grade:

  • Statistically significant adverse effects on English language arts, math, & 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) & disciplinary events in grades K-6 (effect size 0.09) - both statistically significant.


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

  • Both this study & 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.), & funding to implement these practices - as discussed here.

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