Abstract
In the paper, we present the results of partial research, which is part of the three-year project Teacher's understanding of the causes of school failure and the effectiveness of pedagogical interventions. The tool of our research is one task from a didactic test in mathematics for the 2nd year primary school pupils, which was one of the 12 tools in the project to identify pupils at risk of school failure.
The task was solved by a total of 587 pupils and almost one third of them made some mistake. We classified the wrong solutions into 9 groups.
We describe the mistakes and look for their causes. In the discussion section, we propose some re-educational steps.
To assess the situation in Czech schools, we also use information from semi-structured interviews with six inservice teachers.