The fourth phase of a longitudinal study focusing on the cognitive and language development of children in a primary-grade Spanish immersion program (SIP) is reported. Subjects were the remaining 13 members of an SIP cohort beginning in 1987, 15 members of a standard program comparison classroom, 18 members of another class in the 1987 SIP cohort, 37 members of a second SIP cohort, and 17 members of a same-grade standard-program comparison group. Classroom observations were made in fall 1987 (first SIP cohort only) and in the spring of 1988, 1989, and 1990. The children were tested individually on three measures, including: a test of nonverbal problem-solving ability, an English vocabulary measure, and a Spanish vocabulary test. Results indicate that while the SIP children demonstrated significant gains in nonverbal problem-solving over comparison classrooms between the first and second observations in grade 2 and maintained their gains at grade 3, the difference had attenuated by grade 4. No significant differences in native language development were found at grade 4, despite instruction almost exclusively in Spanish for 2 and 3 years. It is concluded that a common underlying linguistic proficiency facilitates transfer of skills from the first to second language. A 39-item bibliography is included. (MSE)