This article introduces a new computer conferencing metric called Scan Rate, which is a measure of students' and instructors' online reading speed. The term "scan" refers to the practice of either skimming through a message at an unusually rapid pace or reading a message partially and then stopping before the end is reached. It is proposed that the Scan Rate metric offers a useful way of monitoring how thoroughly students attend to the messages they read. Four analyses illustrate the utility of the metric. These reveal that (1) scan rates increase with message size, (2) students are more likely to scan the messages of their peers than messages written by their instructor, (3) students engage in scanning practices more frequently than instructors, and (4) scan rates are partially a function of class size and class configuration. (Contains 1 table and 4 figures.)