If you’re a believer in universal preschool, as am I, and if you believe this research released last week on the benefits of preschool is valid, as do I, and if you believe the Perry Preschool research is solid, as do I, the answer would seem simple: Of course boys benefited academically.

Actually, the primary benefit the boys drew from Perry was getting arrested less often than the control group. As an academic savior, Perry was less than a success for boys. All those academic gains you’ve seen listed for the Perry treatment group over the years (on-time high school graduation was the measure) looked good only because they mixed girls and boys in the research. Inconvenient truth: Only the girls experienced that boost in on-time graduation.

That fact first became known to me a couple of years ago when I moderated a preschool panel at the National Education Writers Association annual gathering, this time in Los Angeles. One of the panelists was Perry lifetime chronicler Larry Schweinhart. Over the course of several email exchanges, he laid out the problem for me.

“Teachers cemented this improvement in place for girls, but not boys, by having more of the girls continue on grade in regular classes rather than retaining them in grade or assigning them to special education classes for mental impairment.”

This doesn’t mean the boys weren’t helped by the Perry Preschool. But that boost didn’t stick for the boys in the same way it stuck for the girls.

Another cautionary note about boys and preschool comes from this Yale study concluding that boys are 4.5 times more likely to get expelled from preschool. For most of us, this was the first time we even realized kids got expelled from preschool. That happens because preschool operators have greater freedom to expell students than public elementary schools.

The final cautionary note is anecdotal, coming from elementary school principals I’ve interviewed who placed their sons into preschool and later regretted it. Those preschools were pushing hard on literacy skills at a developmental time when their sons weren’t ready, they said. As a result, their sons developed an aversion to reading that persisted through the elementary years. I think it’s fair to say that researchers have confirmed what any parent already knows, which is that their daughters develop literacy skills earlier than their sons.

Preschool researchers I trust assure me that boys are in fact helped by preschool, as long as parents choose preschools that know the difference between nuturing school readiness skills and drilling children on those skills. To me, all this adds up to a cautionary note: When writing about preschool research showing the benefits passed along to children, always ask for gender breakdowns.