This study examines the effects of public preschool expenditures on the math and science scores of 4th graders, holding constant child, family, and school characteristics, other relevant social expenditures, and country and year effects, in 7 Organisation for Economic Co-operation and Development (OECD) countries--Australia, Japan, the Netherlands, New Zealand, Norway, UK, and USA--using data from the 1995 and 2003 Trends in International Mathematics and Science Study (TIMSS). Our results indicate that there are small but significant positive effects of public preschool expenditures on the math and science scores of 4th graders and that preschool expenditures reduce the risk of children scoring at the low level of proficiency. We also find some evidence that children from low-resource homes and homes where the test language is not always spoken may tend to gain more from increased public preschool expenditures than other children. (Contains 5 tables and 5 notes.)