We consider the effects of daytime fasting by pregnant women during the lunar month of Ramadan on their children's test scores at age seven. Using English register data, we find that scores are 0.05 to 0.08 standard deviations lower for Pakistani and Bangladeshi students exposed to Ramadan in early pregnancy. These estimates are downward biased to the extent that Ramadan is not universally observed. We conclude that the effects of prenatal investments on test scores are comparable to many conventional educational interventions but are likely to be more cost effective and less subject to "fade out".