When causal inferences are to be synthesized across multiple studies, efforts to establish the magnitude of a causal effect should be balanced by an effort to evaluate the generalizability of the effect. The evaluation of generalizability depends on two factors that are given little attention in current syntheses: construct validity and external…

The inclusion of young children with disabilities has remained a function of the Head Start program since its inception in the 1960s when the United States Congress mandated that children with disabilities comprise 10% of the Head Start enrollment (Zigler & Styfco, 2000). Standardized, norm-referenced tests used to identify children with…