In this study, we examine the effect of religiosity as measured by attendance at religious services on religious school choice. Particular attention is given to the possibly endogenous relationship between school choice and religiosity. We find that religiosity has an important causal effect on the demand for parochial schools. It is also shown that religiosity is substantially biased downward in OLS and probit estimates of parochial school choice. Finally, we discuss the implications of our findings for estimating the treatment effect of private school attendance on student outcomes. (Contains 4 tables and 4 notes.)