Differences in cognitive developmental level and reading achievement of elementary school children in multiage programming and traditional classrooms were explored. There is controversy regarding the benefit of multiage classrooms for learning academic subjects. According to previous research (e.g., Almy, Chittenden, & Miller, 1967; Brekke, Williams, & Harlow, 1973; Cromey, 1999), cognitive developmental level, reading achievement, and classroom type all seem to be related entities. This study assesses the effects of multiage classrooms compared to traditional classrooms on cognitive developmental level and reading ability of kindergartners, first graders, and second graders. The effects of cognitive developmental level on reading ability were also explored. The results support the connections among cognitive developmental level, reading ability, and classroom type.