Dimensional comparisons are comparisons of one's accomplishments between two domains (e.g., comparisons between math and verbal achievements) that affect our self-perceptions in the domains compared with each other. In particular, dimensional comparisons explain the seemingly paradoxical finding, described in the internal/external frame of reference (I/E) model, that students' math (verbal) achievement has a negative effect on their verbal (math) self-concept (dimensional comparison effect), while controlling for the positive effect of verbal (math) achievement on verbal (math) self-concept (social comparison effect). The present study is the first to examine awareness of dimensional and social comparisons by testing the I/E model with implicit and explicit self-concepts. Using a sample of 795 students from Germany, we measured students' implicit self-concepts using a go/no-go association task. Students' explicit self-concepts were measured using common rating scales. Overall, we were able to replicate the I/E model relations (negative dimensional comparison effects, positive social comparison effects) with both kinds of self-concept operationalization, suggesting that dimensional and social comparisons are also performed unconsciously. The effects of students' achievements on their explicit self-concepts were usually stronger than those on their implicit self-concepts. However, whereas (in line with prior studies of the I/E model) the dimensional comparison effects were significantly weaker than the social comparison effects in the I/E model with explicit self-concepts, dimensional and social comparison effects were equally strong in the I/E model with implicit self-concepts. This finding emphasizes the relative importance of dimensional comparisons in the process of implicit self-concept formation.