In modern society technology is widely used and, with the digitization of many services, this is an upward trend. Therefore, computational thinking (CT) is an increasingly important concept; an aspect that is being reflected on educational policies and the extracurricular offer of different countries. This study aims to look at the efficacy of private after-school extracurricular robotics activities, controlling fluid intelligence (Gf), a determining aspect in solving novel problems. A sample of 112 fifth-grade Spanish students was chosen, who completed two tests, the computational thinking test (CTt) (Román-González, 2016) and the KBIT fluid intelligence subtest (Kaufman, 1990). The results showed a great influence of Gf on the prediction of CT and significant differences between the students that had not attended after-school extracurricular classes and those that had attended for two or more years. Thus, this study substantiates the effectiveness of private extracurricular classes in promoting CT in the long term. Given the importance of CT nowadays, legislators should consider to include CT in compulsory education because private extracurricular classes could promote inequity.