This research investigated key factors in learning conceptual material about statistics, and tested the effect of variability during retrieval practice. The goal was to build a model of learning for schedule-based interventions. Participants (
= 230) completed multiple reading and test trials with fill in the blank sentences about basic statistics concepts. The experiment was a 2 (trial type: read or drill) × 3 (learning trial spacing: wide medium, or narrow) × 2 (fill-in term during learning: variable or constant) × 2 (fill-in term during posttest: variable or constant) within-subjects design. The model of the results captures the data with recent and long-term components to explain posttest transfer and the testing and spacing effects. These results, and data on the conceptual confusions amongst statistical terms, are discussed with respect to implications for future intelligent learning systems.