An experiment was carried out to determine the effect of several elements of mastery learning on student achievement in an undergraduate course on curriculum development and instruction, which is a less sequential course than the type of courses used in prior studies. Learning in a less sequential course can be facilitated by previous learning, but the lack of prerequisites does not obstruct learning. Students were randomly assigned to three groups: conventional teaching methods; enhancing cognitive entry behavior plus conventional teaching methods; and feedback/corrective procedures, enhancing cognitive entry behaviors, and conventional teaching methods. The combination of feedback/corrective procedures and initial enhancement of cognitive prerequisities was significantly more effective than using only enhancement of cognitive prerequisites, which in turn was significantly more effective than using conventional methods. The results indicate that using a combination of alterable variables effectively in the teaching-learning process may solve the ''two sigma problem'' in less sequential subject series and at the university level.