According to researchers at Stanford and U.C. Berkeley, yes.  The findings in this article are being considered heavily by lawmakers as they push for universal preschool in various states across the U.S. 

This one was a little discouraging, especially for a mom like me who visited at least 10 preschools before making a choice.  Personally, we’ve seen nothing but positive development in our kids since they started preschool, but this study is looking at overall trends, and parents should definitely be aware of the results.