The relationship between the construct of mental attention and "giftedness" is not well established. Gifted individuals could make effective use of their executive functions and this could be related to their mental attentional capacity. The dialectic constructivist model developed by Pascual-Leone introduced the concept of mental attention or "effort", relating it to mental capacity. The aim of this study is to investigate whether the measurement of mental capacity (M-measurement) is differential for a group of children with high IQs. 110 students between 4 and 18 years old participated in this study. Some were Gifted (n=70) and others Non-Gifted (n=40). Wechsler-R Scale and the Figural Intersection Test were administered to all participants. An interesting pattern was found in the younger groups. The gifted scored higher than the non-gifted in the Figural Intersection Test and much higher than their theoretical M. The non-gifted scored quite close to their theoretical M (based on age). In the oldest group, the gifted again achieved higher scores, but now they scored at the theoretical level, and the non-gifted underperformed. (Contains 2 figures and 3 tables.)