To help with the improvement in professional learning of teachers the opinions of 190 elementary school teachers on developmental leadership, cooperation among teachers, internalization of school objectives, self-efficacy, and teachers’ participation in professional activities were sought using a questionnaire constructed on the basis of the study’s theoretical foundation and previous research. The analyses of the so collected data reveal that cooperation among teachers, self-efficacy, and internalization of school objectives as one’s own are the most effective factors on teachers’ participation in professional learning activities. Developmental leadership, not only affects cooperation among teachers, but coupled with cooperative decision making, affects teachers’ professional learning. Finally, it is concluded that teachers’ participation in professional learning activities is influenced by systemic and out-of-school factors as well, that need further research.