Fig. 1. The %<Gain> vs. %<Pretest> score for 62 courses, enrolling a total of 6542 students. Here, %<Gain> = %<posttest> – %<pretest>, where the angle brackets “<....>” indicate an "average" over all students in the course. Points for high school (HS), college (COLL), and university (UNIV) courses are shown in green for Interactive Engagement (IE) and in red for Traditional (T) courses. The straight negative-slope lines are lines of constant "average normalized gain" <g>. The two dashed purple lines show that most IE courses achieved <g>’s between 0.34 and 0.69. The definition of <g>, and its justification as an index of course effectiveness, is discussed in the text. The average of <g>’s for the 48 IE courses is <<g>> _48IE = 0.48 ± 0.14 (standard deviation) while the average of <g>’s for the 14 T courses is <<g>> _14T = 0.23 ± 0.04 (sd). Here, the double angle brackets “<<....>>” indicate an "average of averages." (Same data points and scales as in Fig. 1 of Hake 1998a.)