In order to foster self-regulated learning (SRL), teachers should provide students with learning strategies, as well as with constructivist learning environments that allow them to self-regulate their learning. These two components complement each other. When investigating teachers’ promotion of SRL, not only teacher behavior, but also teachers’ beliefs as well as their knowledge about SRL are relevant aspects to consider. Therefore, this study seeks to examine teachers’ knowledge and beliefs on promoting SRL, as well as their predictive value on teachers’ promotion of SRL in the classroom. Forty-seven primary school teachers completed questionnaires on knowledge and beliefs towards both components of the promotion of SRL: strategy instruction and a constructivist learning environment. In addition, teachers had to answer open-ended questions on their understanding of SRL, as well as their implementation of SRL in their classroom. The results show that teachers are more positive towards constructivist than towards SRL (teacher beliefs), and most teachers mentioned characteristics of constructivist learning environments, while only few teachers addressed strategy instruction when being asked about their understanding of SRL (teacher knowledge). Moreover, teacher beliefs are the only predictor for teacher behavior. The results indicate how teacher education could support teachers to learn how to promote SRL effectively.