In this paper we will argue that quasi-experiments can be equated to theoretical randomized experiments based on the extent of statistical control for confounding factors accounted for by measures such as a pre-test. That is, we use theoretical randomization as a baseline for evaluating the effective control of any study instead of using a single randomized empirical study as a gold standard against which to compare others. Ultimately, we will report that the quasi-experiment in Hong and Raudenbush (2005) used to infer an effect of kindergarten retention on reading achievement crosses the threshold for equivalence with a theoretical randomized study. We then develop a general formula and guidelines for equating quasi-experiments and randomized experiments based on the degree of statistical control achieved. In the discussion we emphasize the validity of causal inferences from quasi-experiments. 2