Scores from computer-based tests are increasingly used to inform a variety of school- and student-level decisions. An underlying assumption is that the associated scores represent effortful responding by each student with respect to the tasks presented. An innovative method for examining evidence for this assumption involves an examination of item response times to detect rapid guessing behavior. If such behavior is present for a particular student across many items, the score is considered invalid due to low test-taking effort (TTE). Drawing on Eccles' expectancy-value theory, this study explored the prevalence of low TTE among middle school students during a computer adaptive test in reading, as well as demographic and motivational correlates of low TTE. Results suggested a prevalence rate of low TTE of 7%. Low TTE was particularly common among males and those with high cost value perceptions. Implications for research and practice are discussed.