This study examined the joint effects of social comparisons (comparisons of one's own achievements with those of others), dimensional comparisons (comparisons of one's own achievements in different domains), and temporal comparisons (comparisons of one's own achievements across time) on students' ability assessments. For the first time a longitudinal experiment, using N = 411 students from German universities, was conducted to examine these comparison effects on students' own self-concepts, their inferred self-concepts of a peer, and their own assessments of a peer's abilities in the figural and verbal domains. As expected, significant social and dimensional comparison effects on the different kinds of ability ratings were found. However, contrary to assumptions, most temporal comparison effects were nonsignificant. The social comparison effects were stronger than the dimensional and temporal comparison effects. Moreover, the social comparison effects were stronger, while one dimensional comparison effect was weaker, when students assessed their peers' abilities, rather than inferring the self-concepts of their peers.