The aim of this study was to examine differences in self-efficacy in the learning process, subjective task value, and test anxiety among students between the subjects of Croatian language and Mathematics, as well as differences in students' perceptions of instructional humor and supportive teacher-student relationships between these subjects. Furthermore, the study aimed to investigate the predictive validity of these variables on final grades in these subjects. The research was conducted using an online questionnaire on a sample of 319 students (25.7% males) attending a grammar school in the city of Zagreb. The results show several significant differences between the Croatian language and Mathematics in motivational and teacher-related variables. By combining all used variables in the final step of hierarchical regression analysis we explained 46% of the total variance in the final grade in Mathematics and 35% of the total variance in the final grade in the Croatian language. Self-efficacy in the learning process and supportive teacher-student relationships were positive predictors, while test anxiety was a negative predictor of the final grade in both subjects. Subjective task value was a significant positive predictor of the final grade in Mathematics, but it did not show a significant contribution to explaining the final grade in the Croatian language. Appropriate and inappropriate humor styles were not statistically significant in explaining the overall variance of the final grade in both subjects. The obtained results indicate a somewhat different relationship between motivational factors in these two subjects and a complex relationship between instructional humor and educational outcomes that needs further investigation.