The largest ever randomized controlled experiment to study the benefits of pre-kindergarten found it hurt more than it helped.

The study looked at families with an income below the poverty line who wanted to enroll their kids in an academic focused pre-kindergarten. Because of limited space, attendees were randomly selected and those who were denied a spot made up the control group of the experiment.

On academic measures, the pre-K group started off performing better. But the control group caught up quickly and “by third grade, the control group performed better on all academic measures than the pre-K group.”

But that’s not all— “the pre-K group were significantly more likely to have been diagnosed with a learning disorder and had a higher rate of school rule violations than those in the control group.”

By sixth grade, pre-K kids were 74% more likely to have been diagnosed with a learning disorder that needed an IEP (individualized education plan).

The control group kids also got in significantly less trouble throughout elementary school.

So maybe think twice before surrendering more of your kids’ time to public schools.