Teachers are the key factor of learning. But what are the characteristics of teachers that are associated with better students’ results? The variables that we can easily measure, such as the years of schooling, have not been associated with higher learning. Neither does additional experience have a proven impact. However, the first years of experience in the classroom do influence teacher quality. Also, the knowledge of the subject that he/she teaches, measured by the scores that the teachers obtain in tests, and their accreditations in a demanding teacher accreditation system, have shown positive effects on student achievement. There are various policies adopted by successful systems. First: successful systems set clear student learning standards or goals. These guide the teachers and tell them what knowledge and skills they and the students must acquire to then advance through each educational system grade. These standards also include skills that must be demonstrated by the effective teacher to make sure that their students are learning in the classroom. Second: countries that consistently top the international learning test strive to attract the best teachers, which is one of the factors associated with good performance. Third: proper training, both before entering the classroom, as well as in-service, is important to improving teacher effectiveness. Fourth: the education systems must create teacher education systems to make sure that the most effective teachers teach in areas where their skills are most needed, that is, in schools located in areas that serve the most vulnerable populations. The teachers’ skills and characteristics must be adapted to teach students from different cultural and linguistic experiences and different skills,from those with special needs, including physical and learning disabilities, to those students with exceptional talents. To ensure that all students have access to effective teachers it is important, in the first place, to transform the teaching career, and to attract, develop, encourage, and retain the best professionals.