Can defaults change behavior when post-intervention effort is required?

Nothing is known about the effectiveness of defaults when moving the target outcome requires substantial post-intervention effort. With two field experiments in higher education, we investigate howdefaults fare in such situations. We change the exam signup procedure to "opt-out" for a single exam (Exp 1), and for many exams (Exp2). Both interventions increase sign-up at the beginning of the semester. Downstream, at the end of the semester, opt-out increases task completion (exam participation) for a single exam but not for many exams. For the single exam, effects on passing (successful task completion) are heterogeneous: students responsive to unrelated university requests convert increased sign-ups into passed exams. For non-responsive students, increased sign-ups result in failed exams due to no-shows. Defaults can thus be effective but need to be carefully targeted.