Assessing a student's acquisition rates (ARs) is a reliable way to determine how many new words should be taught in one lesson without reducing retention. Exceeding a student's AR can result in frustration and problem behaviors. The purpose of this study was to examine the effect of AR on the off-task behavior of kindergarten students while participating in a commonly used sight-word instruction video. Participants included 39 kindergarten students whose ARs were assessed before showing the sight-word video. Behavior was measured as on- and off-task using momentary time-sampling with 10-s intervals. Results indicated that students' time off task increased after exceeding their ARs, with a noticeable immediate increase. The implications and limitations of these results are discussed.