This study represents a continuation of a longitudinal assessment of the effectiveness of a Montessori and Responsive Environment preschool program sponsored by the Arlington Public Schools. The Metropolitan Readiness Test, the Caldwell Cooperative Preschool Inventory, and the Peabody Picture Vocabulary Test were used to assess the academic achievement and intellectual development of 3-, 4-, and 5-year-old children with the Montessori or Responsive Environment experiences and those with no preschool experience at the end of the regular kindergarten program. The SRA Achievement Series, Grade 1, was used to assess the achievement of children, with and without the Montessori experience, at the end of first grade. Results indicated that children in the regular 5-year-old kindergarten program with prior Montessori experience scored significantly higher on the Caldwell measure than did children without this experience upon entrance into the program. When all of the children with either type of preschool experience were categorized as one treatment group, results showed that these children scored higher on the Caldwell measure at the beginning and end of the 5-year-old program than those without the experience. Significant differences in favor of the preschool treatment group were also noted on the pretest of the Caldwell subtests: Personal-Social, Associative, Vocabulary, and Concept Activation-Numerical. It was concluded that early educational preschool experiences can be effective in fostering the academic achievement and maintaining the intellectual development of children. (Author/JMB)