Although intelligence has traditionally been identified as "the ability to learn" (Peterson, 1925), this relationship has been questioned in simple operant learning tasks (Spielberger, 1962). Nevertheless, recent pieces of research have demonstrated a strong and significant correlation between associative learning measures and intelligence (Kaufman, DeYoung, Gray, Brown, & Mackintosh, 2009; Williams, Myerson, & Hale, 2008). The present paper aims to examine the relationship between intelligence and learning, complying with the experimental conditions of discriminative conditioning in a relatively complex free operant task. To that end, a sample of 1600 subjects applying for an "ab initio" Air Traffic Control training course was tested. The task is expected to allow identifying the specific influence of intelligence on the discrimination between stimulus dimensions. The results show how the relation among learning and intelligence strengthen on those trials which are critical in terms of discrimination. (Contains 5 figures and 1 table.)