Fractions are challenging but essential for mathematical learning. Educational technology may support students’ acquisition of fraction concepts. This study investigates underlying cause-and-effect mechanisms, i.e., whether features, e.g., authentic simulations, have a motivating effect in learning situations—resulting in an indirect learning-promoting effect. In a randomized controlled trial with $N=292$ sixth-grade students, we examined the effects of a digital, simulation-based exploration of fractions compared to a paper-based version on students’ subjective task value and their learning gains related to ‘part of many wholes’ concept. Results showed a significant positive effect of the digital, simulation-based exploration on a composite scale of students’ intrinsic value and attainment value. Mediation analysis further indicated that the digital simulation significantly enhanced students’ subjective task value, which in turn significantly improved posttest achievement. Consistent with the mediation hypothesis, we found a significant indirect effect. These findings underscore the importance of integrating features into digital learning environments that enhance student subjective task value in the challenging content area of fractions.
