Mainland China has a highly centralised curriculum development system. A study of two schools in northeast China, one in a rural area and the other in an urban area, indicates that the primary mathematics curriculum has been widely adopted by teachers at the classroom level. Feeling the intense pressure generated by the national mathematics Olympiad, teachers in the urban school tended to give more difficult mathematics problems to their students in the hope that above-average students would perform well in the competition. In the rural school, the ability of students was more varied and generally lower. Teachers there worked very hard to push their students to meet the national requirements. The driving force behind this was the county-wide public examination in which students' performance was taken as an indicator of teachers' competence. Teachers in both schools also have not taken effective steps to adapt the curriculum for students' individual differences. A comparison of the practices between the teachers in the two schools suggests that teachers' beliefs, their professional knowledge and skills shape their inclination and ability in curriculum adaptation and differentiation. (Contains 5 tables and 4 notes.)