Objective: Validation of a previously published scoring system for the Clock Drawing Test (CDT; Parsey et al., 2011) was conducted to determine psychometric properties of the scoring system in an older adult sample with varying levels of cognitive impairment. Method: Participants were 251 older adults (M = 69.78 years old) divided into diagnostic groups of cognitively healthy (OA; n = 164), mild cognitive impairment (MCI; n = 59), and dementia (AD; n = 28). The CDT was administered with instructions to draw a clock and set the time to “10 minutes after 11.” Using the Modified Rouleau scoring system (Parsey et al., 2011), the total score and individual error scores were compared across diagnostic groups. Results: Total scores were significantly different between diagnostic groups such that the OA scores > MCI scores > AD scores. ROC curves revealed cut-off scores of ≥14 for OA, 12-13 for MCI, and < 11 for AD (AUC range = .531–.835). Measures of sensitivity (.679–.731) and specificity (.582–.942) for Modified Rouleau total scores revealed the ability to distinguish between all groups. Presence of conceptual errors differentiated all groups from each other, with approximately 25% of MCI and >50% of the AD participants committing at least one conceptual error (e.g., misrepresentation of time). Presence of more than two hands and/or evidence of hemineglect were indicative of greater cognitive impairment and generally not seen in the OA group. Conclusion: Current findings were consistent with initial analyses of the Modified Rouleau scoring system, demonstrating support and validation for detecting error patterns in clock drawings that distinguish levels of cognitive functioning in older adults.