A socioeconomic status (SES)-related achievement gap in mathematics emerges in children from many countries before school entry, persists in primary school, and imposes challenges for education systems worldwide. In response, the United Nations' sustainable development goals include universal access to quality preschool education to support universal numeracy. A generalizability study of the effectiveness of an early mathematics intervention was conducted for low-SES Turkish preschool children (33 boys, 27 girls; Mage = 4.32). Classrooms were randomly assigned to treatment (Pre-K Mathematics) or control conditions. Children's early mathematical knowledge was assessed by the Child Math Assessment. A statistically significant positive impact was found (ES = 1.32). This indicates some generalizability of the intervention and supports the feasibility of using early intervention to achieve UN goals.