Fig. 1

A) Efficiency graphs (EG). To produce EGs, the data were standardized by student (z-scores), aggregated by session, and mean session values were plotted. Sessions above the y = x line were considered more efficient, sessions below the line less efficient. The position on the graph with respect to the line can also be expressed as efficiency metric E = (y – x)/√2 [23]

B) Comparing cognitive load- and time-based efficiency in year 1. Each dot represents one session. Sessions were ordered alphabetically and then numbered from 1–97. To better visualize the position of each session with respect to the line, we colored each dot with the value of the efficiency metric E, for time or cognitive load respectively. In year 1, 25 out of 97 sessions were very efficient (E ≥ 0.5) in either time (n = 7), cognitive load (n = 7), or both (n = 11). Similarly, 27 out 97 sessions were quite inefficient (defined as E ≤ − 0.5) in either time (n = 9), or cognitive load (n = 11), or both (n = 7)

C) Alignment of prep time with cognitive load over the years. Cognitive load based EGs for year 1 and year 3 were plotted. Each dot represents one session color-coded by prep time in hours. Graphs show a change from year 1 to year 3 in better alignment of prep time with most difficult materials

D) EGs with Cluster overlay. Cognitive load- and time-based efficiency graphs from panel B were overlayed with the cluster denomination. E) and F) Examples of iterative changes to individual sessions from year 1 to 3 in two different disciplines. The trail line illustrates the change in position on the graph over the years. The line starts with year 1. The end position in year 3 is indicated by the circular marker.