This study aimed to examine the effects of intervention through a cognitive educational program based on previous research and conducted it on a class of nursery preschoolers. To examine the effects of the intervention, two measures of cognitive abilities (Flanker task / PASS Rating Scale) were administered pre- and post-intervention. We analyzed the activity review sheets filled by children after each session. As a result, the size of interference effects on the response time of the Flanker task in post-intervention decreased compared with that in pre-intervention and the scores of the PASS Rating Scale in post-intervention were higher than that in pre-intervention. Additionally, analyses of the activity review sheets indicated that the descriptions of “content of activity” and “strategy” tended to increase as the sessions progressed. Changes in measures of cognitive abilities suggest that the intervention played an important part in enhancing preschoolers’ cognitive abilities. The result of reflection suggests the fact that we actively provided opportunities to interact with instructors and classmates while verbalizing the contents and strategies of activities during sessions. These results suggest the positive impact of class-wide intervention of cognitive enhancement programs among preschoolers.