Another popular study followed the Chicago Child-Parent-Centers. Like the Perry Preschool Program, this program was targeted, so it aimed to serve disadvantaged and at-risk student populations. The program returned money to the educational system by reducing the rate of students that needed special education and curbing grade repetitions. The program had a benefit-cost ratio of about 10.83 (Karoly 46). Critics of the Chicago CPC study cite potential bias from the lack of data collected by the students who dropped out of the program. Additionally, the program was a relatively small study which leads to questions of whether the data could be replicated on a widespread scale