A recent study 
finds that pre-kindergarten’s academic effects disappear by spring of
first grade, behavioral problems that result from pre-k programs
endure, but the authors want more money devoted to disadvantaged
children and those at schools with “low levels of academic instruction.”

Can someone explain this?

Or this–

As a possible explanation for the behavioral effect, the authors
note that pre-kindergarten programs usually have relatively high
quality, as indicated by teacher education and pay, and probably are
more academically oriented. This emphasis on basic skills, such as
reading and math, may lead to a less positive social climate, with
children creceiving less individual attention and more punitive
discipline.

Higher quality preschools are to blame for behavioral problems?