THE LESS SCHOOL THE BETTER:

By the end of kindergarten, the control children had caught up to the TN‐VPK [preschool] children and there were no longer significant differences between them on any achievement measures. The same result was obtained at the end of first grade using both composite achievement measures.

In second grade, however, the groups began to diverge with the TN‐VPK children scoring lower than the control children on most of the measures. The differences were significant on both achievement composite measures and on the math subtests.

In other words, after some period of time the children who had preschool actually did worse.  I found this interesting too:

First grade teachers rated the TN‐VPK children as less well prepared for school, having poorer work skills in the classrooms, and feeling more negative about school.

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