Background:
The introduction of including chess into school activities has recently attracted the attention of policy makers, teachers and researchers. Chess has been claimed to be an effective tool to enhance children’s mathematical abilities, because the game – similarly to mathematical tasks – demands children the use of heuristics to correctly interpret problem situations, and select the appropriate course of actions.

Material and methods:
In this study, 931 primary school pupils were recruited and assigned to either one of two treatment groups attending chess lessons, or a control group, and all were tested on their mathematical problem-solving abilities. The two treatment groups differed with regard to the teaching method adopted: The trainers (chess instructors) of one group taught the pupils heuristics to solve chess problems, whereas the trainers (school teachers) of the other group did not teach any chess-specific problem-solving heuristic.

Results:
The results showed that the chess instructors’ group outperformed the other two groups in mathematical problem-solving ability, whereas no difference was found between the school teachers' and the control groups.

Conclusions:
These results foster the hypothesis that a specific type of chess training improves children’s mathematical skills, and uphold the idea that teaching general heuristics is an effective way to promote transfer of learning.