This study examined factors anticipating adolescents’ (N = 232) adherence and dropout in an online acceptance and commitment therapy (ACT) intervention targeted at promoting well-being during the COVID-19 pandemic. First, results showed that adolescents with high academic achievement and educational expectations were more likely to participate in the induction meeting and start the program. Second, adolescents in the human-supported model fulfilled the adherence criteria more often than adolescents supported by virtual coach only. Finally, though male participants were less likely to participate in the study, participants who started the online program were likely to adhere to it regardless of gender.