Among four year-groups of children in a school system (266 girls, 284 boys), 4 percenthad a reading disability (IQ ≥ 85), and 2.7 percent were “slow learners” (IQ < 85). Reading disabled boys tended to be later born in their families, and 40 percent of those born in the local area came from the 10.8 percent of boys born when the mean monthly climatic temperature was ≥ 71°F (mainly July). This was seven times the rate for boys born in cool or moderate months (33°F to 70°F). Lower reading scores were associated with hot birth month temperatures for all socioeconomic groups. Possible explanations are discussed.
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