Based on two different types of researches, this article explores how teachers’ judgements for the school performance of pupils in the last three grades of the elementary school, relate to their performance in written assessment tests. The aim was to examine the teachers’ judgement accuracy and reliability, and investigate the individual factors that influence them. A series of tests was assigned to the pupils and a variety of writing and word processing skills was measured. The classroom teachers assessed the pupils based on their responses to the objectives of the curriculum in all subjects. They put a numerical score from 5 to 10. Also, the teachers assessed the pupils with Learning Disabilities in the language skills, as well as for the occurrence or not of specific behavioral problems, by completing a Likert 5-point questionnaire. In the first study, the results showed significant correlations, for more tests, at a high level. In the second study, they were low and medium. It seems that teachers evaluate the school performance of their pupils significantly based on their performance in writing tests. However, their judgments about school performance are broader and assess pupils’ overall ability in a variety of subjects. The correlations between the two measurements appear to be influenced by several factors related to the class level or school, the pupils' abilities, the type of test, and the way of assessment.