In the process of reforming education, the issue of assessment children’s educational achievements becomes of paramount importance. The article goes on to discuss the guiding principles under which educational achievements of schoolchildren are evaluated within the context of reforming primary education. The authors have outlined the principles of positivity, regularity, optimality, comprehensiveness, as well as criteria-based approach, individualized analysis of the problem, fixing on the student’s personal progress and collaborative evaluation. Considering the above-mentioned principles, the educator can be provided with the information which helps to predict and further adjust the educational process.