The COVID-19 pandemic has drastically reduced physical activity (PA) behaviors of many people. Physical education (PE) is considered one of the privileged instruments to promote youths' PA. We aimed to investigate the effects of lockdown on PE teachers' behaviors promoting their students' out-of-school PA and differences between three European countries. A sample of 1146 PE teachers (59.5% females) from France, Italy, and Turkey answered an online questionnaire about guiding students to engage in out-of-school PA, helping them to set PA goals, encouraging in self-monitoring PA, the pedagogical formats of these behaviors and feedback asked to students. RM-MANCOVAs were performed with a two-time (before and during the lockdown), three country (France, Italy, Turkey), two gender factorial design, using teaching years and perceived health as covariates. A significant multivariate main effect time × country × gender (p < 0.001) was reported for the behaviors promoting students' PA, with French and Italian teachers increasing some behaviors, while Turkish teachers showing opposite trends. Significant multivariate main effects time × country were found for formats supporting the behaviors (p < 0.001) and for asked feedback formats (p < 0.001). The massive contextual change imposed by lockdown caused different reactions in teachers from the three countries. Findings are informative for PA promotion and PE teachers' education.