Analyzing data from a fifteen-year follow-up survey of high school students originally surveyed in 1957-58 and resurveyed in 1973-74, this paper examines the effects of the timing of marriage and first birth on subsequent childspacing, holding constant the effects of other variables that may be sources of spuriousness. The results suggest that age at first marriage has a causal effect on the occurrence of a short first birth interval and that age at first marriage and premarital pregnancy interact in their effect on the occurrence of a short second birth interval. Age at first marriage has no causal effect on the spacing of the second birth for those whose first child was maritally conceived. The spacing of the first birth, however, appears to have a causal effect on the spacing of the second.