Although one would expect the most effective programs to be those with the most intense and long-lasting interventions, com- parisons among the longitudinal research studies allow only gen- eral conclusions regarding the benefits of program intensity and duration (McKey et al., 1985; Ramey et al., 1985). As Tables 4-1 and 4-2 show, some effective programs offered only a half-day program during the school year, and others began intervention in infancy and continued through to elementary school; one of these continued intervention in the early grades for some of the chil- dren. Another study began in preschool but provided interven- tion into the elementary school. Two of the studies that began in infancy are the only longitudinal studies to find lasting IQ gains for the experimental group, with the exception of the Harlem Study (where design limitations raise questions about this find- ing). The Harlem Study offered one-to-one tutoring to boys in Harlem twice a week at age 2 or 3. In addition, the Perry Project that offered one or two years of preschool intervention has shown remarkable effects of the program into adulthood (Schweinhart et al., 1993). Given the number of ways in which intensity and con- tinuity of service can vary, these must be viewed as more than a simple function of time in a program. Obviously, two 1-hour ses- sions per week one-on-one with a teacher is intensive in a differ- ent way than 6-10 hours every weekday in a classroom. Other programs have sought to increase intensity with lower ratios, home visiting components, and high levels of engagement.