The Dutch Educational Opportunity Program was begun in 1988 to improve educational achievement of Dutch low socioeconomic status (SES) children and children from ethnic minorities. A longitudinal study was done of children in grades 4, 6, and 8 at 700 primary schools. Every 2 years the children were tested for intelligence, arithmetic, and Dutch language. After evaluation of two testing periods, it appears that achievement among the disadvantaged groups has not improved in comparison with a representative reference group. However, when analyzing the data in more detail, taking into account the children's SES, ethnic background, and intelligence, remarkable differences can be found in effectiveness between schools in arithmetic and Dutch language proficiency. Data were gathered on about 50,000 students tested in grade 4, 6, and 8 in 1988 and in 1990 in about 600 primary schools. Results suggest that in the future the quality of education should be monitored closely. Many of the failures in helping disadvantaged children result from the misconception that education should be adapted to the development level of the child. Education should be modeled around the concept that all students can reach desired goals, but some may require more time and instruction. (JPT)