This study investigates the relationship between chronic poor health and school outcomes among children. A simultaneous three-stage least squares model is estimated in which achievement and attendance are endogenous variables. The hypothesis that particular health characteristics are associated with differences in individual school outcomes is confirmed. For example, attendance is affected most by illnesses likely to interfere with school or peer interactions or difficulty doing only strenuous activity. Achievement is lowered by moderate to severe psychologic problems. Including attendance as an endogenous variable increases its significance. Other socioeconomic and school variables, such as mother working, marital status and special schooling, are included in the model. Policy implications are suggested.