The practice of adding game elements to non-gaming educational environments has gained much popularity. Gamification has been found in some studies to increase learner engagement, motivation, and academic performance. However, there is a lack of empirical evidence to prove the effects of gamification in advanced learning technologies like Intelligent Tutoring Systems (ITS). This paper reports the results of an empirical study that included three categories of game elements (goals, assessment and challenges) implemented as badges in the context of SQL-Tutor. The study was conducted in a class under realistic conditions. SQL-Tutor was used voluntarily by 77 undergraduate students enrolled in a second-year database course. Although there were no differences between the experimental and control groups in terms of their interaction with SQL-Tutor and learning outcomes, we found a significant mediating effect of time-on-task on the direct relation between badges and achievement in the gamified condition. We also found evidence that not all students were interested in badges.