Reported associations between season of birth and reading failure suggest medical causationand prevention. The relationship between season of birth and two measures of reading outcome in twocohorts of children (n, = 2411 and n2 = 1972) was studied using %2 tests. None was significant. Logisticregression was used to investigate the joint associations of gender, age at school entrance, and season ofbirth with reading outcome. A significant interaction between reading failure and age category (overage atschool entrance vs correct age) by season of birth was observed. It was shown that this significant interactionwas probably caused by kindergarten entrance cutoff birth dates. Although 67.8% of all overage children hadsummer births, only 15.3% failed in reading, which is not statistically different from the percentage of summer-born, correct-age low readers (13.6%). Results suggest that reported associations may be attributed toselective samples rather than the total population of school children who experience reading failure.