From an early age, children are exposed to mathematical experiences. These experiences influence the child's thinking about his or her abilities to do mathematics. Children who participate in early childhood programs may have experiences that develop positive attitudes toward mathematics. However, not all children have that opportunity. Children who struggle with mathematics may not have developed a strong foundation to support future skills. One approach for early intervention is participation in full-day kindergarten. Considerable research has been conducted on the effectiveness of half-day vs. full-day kindergarten. While there have been attempts to synthesize this research through meta-analysis and narrative reviews, none of the previous studies have focused exclusively on mathematics. Rather, they have focused on general academic or literacy effects of the schedules. The purpose of the proposed study was to investigate whether students who participate in full-day kindergarten have a long-term advantage over half-day kindergarten in mathematic achievement during Grades 1-4, and to examine some of the moderator variables that may influence the effect. The method, which was employed, was a meta- analysis of existing research. These studies showed a statistically significant difference in children's mathematical achievement when they attended full-day kindergarten. Unfortunately, the difference is not long term. Attendance at full-day kindergarten makes a difference in mathematical achievement during kindergarten and first grade. More studies need to be done to investigate reasons why the decline in mathematic achievement occurs after the first grade. Potential areas for future research include teacher training, the mathematics curriculum, and philosophical approaches to teaching.