The present study aimed to compare successful with less successful English as a Foreign Language (EFL) learners regarding their cognitive styles and flexibility, together with the learners’ evaluation of their experience of doing an unfamiliar cognitive test. The sample consists of 60 adult EFL learners (30 successful and 30 less successful), both males and females symmetrically. The homogeneity of participants’ age of onset, socio-economic class, and motivation was also considered. The data was analyzed, using Chi-square and Gamma correlation. Overall, it was revealed that analytical, logical reasoning, reflective, and learning were the most prominent cognitive styles among successful learners. They also showed a considerable cognitive flexibility. On the other hand, less successful learners were inclined to the random style, along with a lower cognitive flexibility. With respect to gender groups, it turned out that females in the successful group were significantly inclined to the reflective and logical reasoning styles and less successful females adopted a random style. Finally, no significant result was found concerning the cognitive test evaluation. The findings of this study may contribute to a wider understanding of EFL success and failure from the viewpoint of cognitive preferences.