Although early diagnosis of developmental delay is important, there are challenges in identifying cognitive status in developing countries because of limited human and financial resources to perform diagnostic tests. Moreover, diagnosis stability of developmental delay in children using neuropsychological tests (NPTs) can remain unsettled. The aim of this study is (1) to verify the effectiveness of a serious game (DoBrain), (2) to identify existing inconsistencies between NPTs, and (3) to explore the potential of the serious game as a complement to diagnostic tools. Eligible children who had completed results of NPTs were selected (n=119/235; 116/235; case, control). With these children’s scores, we performed the Mann- Whitney U test to investigate the effectiveness of the serious game by comparing the improvement of scores in both groups. Among the participants, we additionally selected a case group to identify the potential of the serious game for detecting mild developmental delay. Using the results of the CGI-S as a baseline, we defined the participants whose scores indicated more than mild illness (>=2 points) in at least one area as the suspected group. The score improvement related to memory in case group was greater than that of the control group (p<0.05). Furthermore, four of the NPTs were not inconsistent, and the sensitivity/specificity of DDST-II was the highest score considering CGI-S results as the ground truth (0.43; 0.96). Additionally, games measuring discrimination, velocity, memory, and spatial perception showed statistical significance (p<0.05). This study verifies that the serious game can help specific cognitive areas and suggests that the serious game could be used as a low-cost and unconstrained spatiotemporal alternative to NPTs.