Nearly half of the control - group children did enroll in other preschool programs. (nationalaffairs.com)
Also addressed was the methodological problem arising from the fact that a significant portion of the control - group students attended some sort of other preschool program, meaning there was no true «no preschool» control group. (nationalaffairs.com)
But few other preschool programs were evaluated using randomized trials in the»60s; the Cochrane Collaboration database lists only six trials. (educationnext.org)