A 2-year study was conducted to determine whether service delivery variables in Head Start programs have a direct, positive effect on child performance and home environment. The study sample of 402 four-year-old children was drawn from 12 Head Start programs in Oregon, Washington, and Idaho. The centers represented three types of models: traditional center-based programs, home-based programs, and three different combination center- and home-based programs. Outcomes were measured using a variety of behavioral, developmental, and psychometric scales for children; kindergarten records; interviews with parents; home observations; and parent measures on locus of control, beliefs about child behavior, and social support. Study findings included the following: (1) at the end of the Head Start year (Year 1), the combination models achieved equivalent outcomes as the center- or home-based models; (2) after Year 1, neither the number of center nor home visits was associated with child performance gains; (3) at the end of years 1 and 2 (the kindergarten year), there were no significant differences among the models in improvements in the home environment; however the home-based programs consistently achieved higher scores on measures of home environment; (4) there was no relationship between improvements in the home environment and gains in child performance; and (5) after Year 1, programs within similar models produced different child performance gains, but after Year 2, similar programs produced equivalent gains. (AC)