Using Glass's meta-analysis, of which "effect size" is the fundamental measure, 135 research studies on Ausubel's advance organizer theory were reviewed to determine its effect on learning and retention. Variables, such as grade level, subject area, organizer presentation mode, and ability level were also examined. In most of these studies advance organizers are shown to have a facilitative effect on learning and retention. Advance organizer effect on retention increases with time in relation to the control group. Learning is shown to be more pronounced in college and special education subjects than in primary or secondary school subjects, while primary school subjects show a greater retention increase. Within subject areas, average effect size of the advance organizer on learning and retention is positive, especially in the social sciences for learning and in the physical sciences for retention. For subjects of high ability, the average effect size exceeds that for low ability subjects. Aural mode advance organizer studies show a greater average effect size than written mode, especially for college level subjects. (MH)