The purpose of this study was to study the relationship between beliefs and teaching styles of teachers of mathematics and their students' academic performance in high schools of Yucatan. For this purpose, a questionnaire was administered to 72 high school mathematics teachers and the student academic achievement score of 1241 were used. A significant relationship between beliefs about constructivist teaching and each of the five categories of teaching styles of teachers of mathematics were found, and also relationship between teaching style "Delegator" and student academic achievement were found. It was concluded that mathematics teachers maintain consistency between what they believe and how they teach, so it is important to maintain correspondence between the teaching style and belief system to achieve a satisfactory effect in mathematics and the teaching style "delegator" is associated with better academic performance in mathematics. (Contains 14 tables.)