•It remains unclear what underlies individual differences in adolescents’ willingness to invest cognitive effort within the academic context.•This was examined in a preregistered experimental study within an educationally diverse sample.•Willingness to invest cognitive effort was related to need for cognition and cognitive capacity. There exist large individual differences in students’ willingness to invest cognitive effort within the academic domain. In a preregistered study, we investigated whether individual differences in adolescents’ willingness to invest cognitive effort, as assessed by an experimental effort discounting task, were related to need for cognition, academic motivation and cognitive capacity. We found that adolescents’ willingness to invest cognitive effort was related to need for cognition and cognitive capacity as indexed by task-performance. Our results demonstrate that individual differences in need for cognition and cognitive capacity contribute to differences in adolescents’ cognitive effort-investment, but academic motivation does not.