Higher birth order positions are associated with poorer outcomes due to smaller shares of resources received within the household. Using a sample of Panel Study of Income Dynamics-Child Development Supplement children, we investigate if the negative birth order effect we find in cognitive outcomes is due to unequal allocation of mother and father time investments. Exploiting the presence of siblings in the sample, we show that birth order differences in parental time are mostly driven by between-families variation rather than within-family variation. This finding suggests that birth order effects are unlikely to be driven by differences in quality time spent with either parent.