The Negative Year in School Effect (NYiSE) claims that grade-relative-to-age influences academic self-concept. Being young for your grade is associated with lower self-concept, whereas being old for your grade is associated with higher self-concept. We extend this research in several ways. First, we aim to improve causal claims for the NYiSE by utilizing birth month as an instrumental variable. Using the Longitudinal Study of Australian Youth we find that the NYiSE is negative under instrumental variable regression. Given that NYiSE has focused on math self-concept we show that the effect extends to other measures of math, general academic, and English social comparison. Finally, using General Estimating Equations we show that the NYiSE also has an effect on university entry that is explained by self-beliefs. Our research has policy implications around how children enter school. Further, this research shows that the use of alternative causal modeling strategies is a useful asset to educational research especially when randomized control trials are not yet available or feasible.