As one’s learning results from a complex interplay among his/her cognitive metacognitive and affective domains, the last of which determines the global context where cognition takes place monitored and controlled by metacognition, the learning outcomes may primarily be interpreted in affective terms. Having in mind a strong positive relation between mathematical self and mathematical achievement as well as that a humanistic approach to mathematics teaching/learning would promote higher mathematical self, this study examined whether writing about mathematics in a humanistic context influences mathematical self. This question was answered by comparing mathematical self of twelfth-grade gymnasium (high-school) students who wrote their matura works on mathematical themes (N = 10) with that of their classmates who did that in other subjects (N = 72). A higher mathematical self was found for these ten students, which may be commented with "those who chose to write matura works in mathematics were simply those with higher mathematical self and the writing contributed nothing to the outcome". The values of other control variables measured in grades 9-12 evidence that it is more likely that this finding was influenced by the treatment.