This is an investigation of how (a) performance, (b) self-efficacy strength, and (c) self-evaluation bias and accuracy develop. The learning environment is for the training of arithmetic competences using the computer-based training MatheWarp. To compare the effects of different types of feedback, four training sessions with two versions of MatheWarp were provided. The first version consisted of exercises followed by performance feedback (MatheWarp_KP). The second version offered effort-attributions as part of the feedback (MatheWarp_{KP+effort-attribution}). Forty eight fifth-graders from two classrooms were assigned to these two training conditions on the basis of their pre-test performance. A third fifth grade class (n=23) served as a control group and received no specific training. Performance, self-efficacy strength, self-evaluation bias and accuracy were measured before and after the training sessions. Results show a performance enhancement in the training groups, whereas performance did not change in the control group. However, self-efficacy strength decreased in the MatheWarp _{KP+effort-attribution} group and in the control group; it increased in the MatheWarp_KP group. Self-evaluation accuracy decreased significantly in the training groups, whereas it remained almost constant in the control group.