This article describes mathematics teachers' evaluation practices and the reasoning and beliefs that support those practices. The data were collected in two Portuguese schools representing very different results in the national exams, through semi-structured interviews with mathematics teachers and departmental curriculum coordinators as well as class observations (school year of 2014/2015). The interviews were analysed using content analysis, leading to the conclusion that mathematics teachers' evaluation practices, in both schools, were carried out based on a cyclical process, supported by the perspective that quantitative assessment, through "quantitative tests", enhances students' motivation to study and supports learning and academic success, even though this effect seems to only impact on the "good students".