There is consensus that what a student is evaluated, conditions of their learning and teaching decisions (Darling-Hammond 2001; Himmel, 2003; Shepard, 2006). If we understand the assessment as the process that allows us to obtain evidence of student learning and of the effectiveness of teaching practices, it is clear that a teacher who has strong evaluation competencies will be able to better monitor the learning of his students, make modifications to Its teaching, adjusting it to the specific needs, to give effective feedback; to use the results of evaluations as an input to make evidence-based pedagogical decisions, resulting in better pedagogical practices and better learning (Celman, 2005, Darling-Hammond 2001, Deneen and Brown, 2016). In this context, although classroom assessment is one of the key elements to ensure the achievement of learning, the evidence shows that most teachers in Chile presented the most important shortcomings in this area (Docentemas, 2014), but this reality is not the same in all countries (OECD, 2016). This study analyzes the competence in assessment of 82 primary teachers, with 10.7 years of average experience. The Mertler and Campbell (2005) questionnaire was used. The results show that teachers predominantly dominate aspects associated with the selection of evaluation techniques or instruments, know the types of evaluation (formative and summative and agents) and understand the importance of feedback in the learning process. However, they have a low mastery of ethical principles associated with assessment that directly impact on the consequences of their practices in the learning of their students and on the interpretation and use of standardized test results. The impact of these results on the quality of teaching and initial teacher training is discussed.