Researchers and practitioners see significant potential in using gamified technology-mediated learning (TML) systems to engage users and help them to learn. Yet, existing studies on gamified TML indicate inconsistent findings on the value of these systems. Some studies show higher learning outcomes and engagement while others do not; some demonstrate higher learning outcomes but not higher engagement. Therefore, researchers have called for more nuanced analysis including how individual differences interact with game elements. Specifically, we identify and study two individual differences - gender and achievement goals - in competitive gamified TML designs. We find that gender plays an important moderating role - males engage more and learn better in a competitive learning context than females. Achievement goals help explain differences in users' benefits from gamified TML and how users react to competitive contexts. Our findings indicate that gender and achievement goals are important individual differences to consider in designing gamified TML and explaining its outcomes.