http://www.michiganinbrief.org/edition07/Chapter5/ChildEarlyEd.htm

The longest and most extensive evaluation of an early-childhood program is the High/Scope Perry Preschool Program (Ypsilanti). High/Scope has been following a group of individuals who had attended the preschool program when they were aged three and four. At age 27, they have higher income, fewer arrests, and less welfare participation than do members of a control group that did not participate in the program. Beyond the direct benefits to the children, every dollar invested in the program returned $7.16 to the public in reduced costs of crime, welfare, and remedial education (1993 data).

The Chicago Longitudinal Study follows the education and social development of more than 1,500 low-income children born in 1980 who were served by the Chicago Child-Parent Center. At age 21 the participants, when compared to a peer group who did not receive the center's services, have a 29 percent higher rate of high-school completion, a 42 percent lower rate of juvenile arrest for violent offenses, 41 percent fewer special-education placements, and 51 percent fewer allegations of child abuse and neglect. Every dollar invested in the program returned $7.10 to the public in reduced costs of crime, welfare, and remedial education (2001 data).