The present study aimed to investigate the relative predictive power of teachers' beliefs about cooperative learning, their participation in professional development courses on cooperative learning, emotional exhaustion, and the frequency of cooperative learning implementation before the outbreak of the COVID-19 pandemic for the frequency of cooperative learning implementation during the COVID-19 pandemic. Two hundred and sixty-eight German teachers participated in an online survey in the spring of 2021 (retrospective self-reports, cross-sectional). The study revealed three key findings: first, teachers used cooperative learning significantly less often in face-to-face teaching during the pandemic than before the pandemic. Second, teachers' positive beliefs about cooperative learning and their participation in professional development courses predicted the frequency of cooperative learning implementation before the pandemic. But, third, neither of these aspects of teachers' expertise predicted the implementation of cooperative learning in face-to-face teaching during the pandemic. Only the frequency of implementation before the pandemic predicted implementation during the pandemic which may point to the value of routine in times of crisis. Our findings suggest that the predictive power of aspects of teacher expertise (such as their beliefs) varies with contextual conditions.