Figure 1.

Structure of the randomized controlled trial. To take advantage of the educational merits of the spacing effect, the educational material for each cohort was distributed in three 6-week cycles or repetitions. During each cycle, students were sent a daily (Monday–Saturday) interactive spaced-education e-mail. The 12-week delay in the start of the program for cohort B allowed these students to act as a control group for cohort A: the learning gains of students who had completed 2 cycles of the ISE program in addition to the PD2 course (cohort A) were compared to those students who had only received the PD2 course (cohort B/controls). Thus, this trial structure controlled for students’ learning from the PD2 course and allowed the specific learning gains from ISE to be identified.