in 2014, ccr analytics published the results of their study of 49,467 children assessed in the 2012–2013 school year from 81 head start programs throughout the state of california (more than 50% of the entire california head start population). participation in the study was open to all california head start programs who used the drdp-ps 2010 assessment tool. the study found that providing two years of head start to a child increases the probability by between 13% to 86% that the child will meet age appropriate expectations. regression discontinuity design was used to measure program impact without denying a control group the opportunity to attend head start. the analysis compared three-year-olds enrolled in head start to four-year-olds who returned to head start for their second year. this also eliminated the issue of selection bias because both groups chose to attend head start as three-year-olds.