In 1996, in a journal called the National Teaching & Learning Forum, two professors from Indiana University -- Joan Middendorf and Alan Kalish -- described how research on human attention and retention speaks against the value of long lectures. They cited a 1976 study that detailed the ebbs and flows of students' focus during a typical class period. Breaking the session down minute-by-minute, the study's authors determined that students needed a three- to five-minute period of settling down, which would be followed by 10 to 18 minutes of optimal focus. Then -- no matter how good the teacher or how compelling the subject matter -- there would come a lapse. In the vernacular, the students would "lose it." Attention would eventually return, but in ever briefer packets, falling "to three- or four-minute [spurts] towards the end of a standard lecture," according to the report. This study focused on college students, and of course it was done before the age of texting and tweeting; presumably, the attention spans of younger people today have become even shorter, or certainly more challenged by distractions.

Middendorf and Kalish also cited a study from 1985 which tested students on their recall of facts contained in a 20-minute presentation. While you might expect that recall of the final section of the presentation would be greatest-- the part heard most recently -- in fact the result was strikingly opposite. Students remembered far more of what they'd heard at the very beginning of the lecture. By the 15-minute mark, they'd mostly zoned out. Yet these findings -- which were quite dramatic, consistent and conclusive, and have never yet been refuted -- went largely unapplied in the real world.