Many longitudinal studies entail repeated computerized cognitive testing. However, few of the measures frequently employed for assessing cognitive changes have been examined for within- and between-day retest effects over multiple time points. To address gaps in the repeated cognitive assessment literature, in the current study 20 male undergraduate students completed a computerized cognitive battery 6 times over 3 testing days, each 1 week apart. Performance shifts and test–retest reliability (TRR) varied for different measured variables. Reaction times (RTs) on tasks designed to measure inhibition, switching, and selective attention generally showed good TRR, and few or only gradual improvements over time, suggesting that these measures are suitable for use in repeated testing, and that the inclusion of brief familiarization periods sufficed to resolve initial practice effects. Similar findings were observed for both accuracy and speed on a 2-back working memory task. In contrast, RTs on a basic visuomotor task showed worsening performance across time (likely reflecting boredom effects) and poor TRR, suggesting unsuitability for measuring change in cognitive performance. Cost scores designed to assess inhibition, switching, and selective attention showed poor TRR, as did scoring metrics from visuospatial short-term and working memory tasks (Corsi block paradigm). This low reliability suggests that these scores may not be suitable for use in repeated assessment, and calls into question their validity as measures of the specified cognitive functions. Researchers planning studies entailing computerized assessment of cognitive functioning in healthy young adults should consider the current results when selecting suitable cognitive tasks and measures.