Vanderbilt University’s study of Tennessee’s Voluntary Preschool Program evaluates a low quality early childhood program using a flawed methodology. Randomization was corrupted by noncompliance with the intended experimental protocol. The press release accompanying the report exaggerates the importance of the findings and the quality of the evidence.

Many students assigned to treatment refused to cooperate and the  investigators were forced to use the very same non-experimental methods that they fault other studies for using. Their claim of program effect fadeout is a consequence of the control group catching up, not a decline in performance in the treated.

The real lesson from the program is that you get what you pay for, and Tennessee did not put much into its program. Low quality programs produce weak and even sometimes harmful results.

This study does not refute the strong evidence that high quality preschool programs—criticized by the authors as “too expensive”—more than pay for themselves in terms of ROI.