Recent attention to the causal identification of spending impacts provides improved estimates of spending outcomes in a variety of circumstances, but the estimates are substantially different across studies. Half of the variation in estimated funding impact on test scores and over three-quarters of the variation of impacts on school attainment reflect differences in the true parameters across study contexts. Unfortunately, inability to describe the circumstances underlying effective school spending impedes any attempts to generalize from the extant results to new policy situations.  The evidence indicates that how funds are used is crucial to the outcomes but such factors as targeting of funds or court interventions fail to explain the existing pattern of results.