This study examined the effect of Early Childhood Education (ECE) on the cognitive development of pupils in lower primary education in Kamonyi District, Rwanda. Guided by three objectives-examining the accessibility, availability, and affordability of ECE; identifying aspects of cognitive development; and determining ECE's effect on cognitive growth-the study surveyed 158 respondents from a target population of 260 using descriptive and correlational research designs. Data were analyzed through SPSS and thematic methods. Findings revealed limited accessibility (13.52%) and affordability (mean = 2.85) of ECE. Only 14.7% of teachers reported standard cognitive development in pupils. Regression results showed physical learning environment (R² = 0.414), teacher-pupil interaction (R² = 0.470), and parental involvement (R² = 0.265) significantly influenced cognitive outcomes. The study concludes that poor ECE access negatively affects cognitive development and recommends increased parental enrollment efforts and improved teaching methods.