The present article focuses on teacher competencies as a major factor that impacts student learning. Ultimately, all attempts to improve education converge in the teacher and the quality of his/her work with students. With their teaching methods, their communication and their classroom management, teachers can structure the kind of learning environment that will either promote or hinder learning. The purpose of the article is to analyse research on educational productivity in order to select the most important teacher competencies that are related to student achievement. A model of teacher competencies is developed that serves as a framework for understanding the synergetic effects of teacher competencies on achievement thorough promoting students' cognitive, affective and social processes. The teacher competencies that impact each of the processes are described and their impact on student achievement is explained.