Objective: To examine the diurnal assumptions of the Test of Variables of Attention (TOVA). Method: The present study assessed 122 elementary students aged 5.5 to 10.0 years who were randomly assigned to one of four different groups based on time of administration (M-M: Morning-Morning, M-A: Morning-Afternoon, A-M: Afternoon-Morning, and A-A: Afternoon-Afternoon). Morning administration occurred between 8:00 and 10:00 a.m., and afternoon administration occurred between 1:00 and 3:00 p.m. Results: Reliability was consistent across groups, and there were no significant differences between groups. Classification of the students into ADHD or non-ADHD groups was similar across groups, and the children who were identified as ADHD with the Vanderbilt ADHD Diagnostic Teacher Rating Scale were consistently classified as ADHD on the TOVA regardless of time of day. Conclusion: The results of the present study indicate that the psychometric values of the TOVA remain intact whether its administration was in the morning or afternoon. (Contains 4 tables and 2 figures.)