Understanding students' perceptions of the negative aspects of task engagement, known as cost, can provide new insights regarding how to predict outcomes related to students' learning behavior in school. The present study investigated the associations of cost, compared to and in interaction with self-efficacy and task value, with students' future choice intentions, avoidance intentions, and expected or actual course performance. Associations were assessed separately in two studies and focused on the subject areas of mathematics and English. Participants were students (N = 598 in Study 1 and N = 443 in Study 2) aged between 13 and 18 from two schools in Shanghai, China. For each subject domain in each study, three structural equation models were examined to test the unique associations of cost with outcomes, controlling for self-efficacy and task value. Latent moderated structural equation modeling was used to examine interaction effects among the motivational constructs. Results from two studies demonstrated that cost related negatively to students' course performance in both subject areas. In both studies, cost also interacted with task value in predicting avoidance intentions in both subject areas. Findings highlight the importance of including cost in the expectancy-value framework in order to capture more fully the factors that affect students' motivational dynamics in school.