When initially confronted with the Monty Hall dilemma (MHD), people show a strong tendency to stick with their initial choice, although switching maximizes winning chances. Previous research demonstrated interventions that helped participants to apply the optimal strategy, but still failed to increase participants’ understanding of the MHD solution. An exception is DiBattista’s (2011) digital learning environment study, reporting that the majority of participants who used the learning environment learned to understand the MHD solution. However, a major shortcoming was the methodology, which did not allow to infer causal relations and to conclude which manipulation was most important for participants’ understanding. The aim of the present study was to fill this research gap by conducting a controlled randomized experiment with an analogous digital learning environment. The results showed that receiving explanation about the MHD solution was the most important manipulation to improve understanding. Implications for education in (posterior) probability are discussed.