Willingness to engage in cognitive effort, beyond cognitive abilities, significantly influences academic success. Maladaptive media use, i.e., not aligned with learning goals, may alter reward system functioning and thus the subjective evaluation of effort. This study experimentally examined these effects among high school and university students, drawing on the theory and paradigm of cognitive effort. 94 students (17-26 years, M = 18.79, SD = 1.25) participated in an online experiment on the Inquisit Web platform. They solved working memory (N-back) tasks of varying difficulty, then chose between tasks of different load levels (1, 2, 3) for varying rewards in an effort-discounting paradigm. This was followed by a second stage with point rewards. Participants were randomly assigned to one of three experimental groups: task-oriented social media use, cognitively demanding task, or hedonic social media browsing. After the manipulation, both stages of the discounting paradigm were repeated. Subjective devaluation of rewards showed significant differences between load levels (W1=3179, p<.001; W2=2999, p<.001; W3=3172, p<.001), indicating lower valuation of high-effort tasks even with higher rewards. Effort willingness emerged as a stable trait, along which four clusters were identified through hierarchical analysis of discounting patterns, task performance, and subjective load (NASA-TLX). The clusters reflected distinct strategies: Comfortable (low effort, low performance), Goal-oriented (high effort, high performance), Optimists (challenge-seeking, perceiving tasks as less strenuous), and Deliberate (balanced evaluation, lower preference for high load). Experimental interventions did not produce significant differences between clusters (F1(3)=0.72, p=0.541; F2(3)=1.08, p=0.364; F3(3)=1.17, p=0.326). Findings suggest that dispositional preferences shape decision-making strategies and determine the extent to which maladaptive social media use negatively affects cognitive effort valuation, with implications for understanding motivation and academic success.