On this webpage, http://campustechnology.com/articles/52017/ dated 10/17/2007, an initial study by a professor at Coppin State University in Baltimore indicates that class capture technology that allows students to view lectures online after the fact can improve course retention rates and grades.
Like many colleges whose populations include working students, Coppin State would like to improve retention numbers for many classes; drop rates can average around 30 percent for some courses. In the study, Brittan-Powell found that his face to face classes with no recorded lectures offered after the fact averaged a 71 percent retention rate; when he offered lectures in class and online via Tegrity, that boosted the retention rate to 83 percent, in effect nearly cutting the drop rate in half.
While this study applies to higher ed instead of K-12 in my previous international student achievement accomplishments, I think it supports my hypothesis that the total time of engagement has a positive correlation with academic success. In this study, Tegrity's Campus software can make lectures available at any time to students by automatically capturing, storing and indexing each class for replay over the Internet. It is well known that review and repitition has definite value in learning and recall.