Study Shows Head Start Preschool Programs Don't Measure Up--to what?

My question is: to what do Head Start Preschool Programs not measure up to? Is it really possible that these kids are less prepared after these programs? I think that should cause us to really start re-thinking how our little ones need more than programing to reach their unique potential throughout their lives.

"In January 2010, after four years of “analysis,” the HHS Department finally released the results on Head Start’s impact on first graders. The study found that, compared to their control group peers, Head Start failed to boost students’ cognitive abilities across 41 measures. Moreover, first grade teachers reported that former Head Start students were actually less prepared in math than the non-Head Start students."

http://www.forbes.com/sites/realspin/2012/03/05/parents-deserve-to-know-the-facts-about-head-start/