This study aimed to examine the influence of the 'Board Game Based Cognitive Training Programme' (BGBCTP) on the cognitive development of the second and third graders among primary school children. BGBCTP is based on educational board games for second and third graders and aims to help them develop cognitive skills. Mixed method was used and it was carried out within the framework of embedded design. A quasi-experimental pretest-posttest design was the quantitative data gathering method and a case study was the qualitative one. The participant group consisted of 120 children (60 in the experimental group, 60 in the control group). The interviews were conducted with twenty grade teachers who carried out the training programme in the experimental group. The General Information Form, The Thurstone Primary Mental Abilities Test 7-11 (PMA 7-11) and "Semi-structured Interview Form" were used to collect data. PMA 7-11 was used to statistically test the influence of BGBCTP on the development of second and third graders' cognitive skills. BGBCTP was used by the researcher with the children in the experimental group in a 'regular and controlled' manner, for 12 weeks, 2 days in a week, 1 hour each day (a total of 24 hours), in addition to their daily activities in their regular environment. For quantitative data analysis, the dependent-samples t-test was carried out for in-group comparisons, whereas the independent-samples t-test was used for intergroup comparisons. For qualitative data analysis, a descriptive analysis approach was used. The quantitative research findings indicated that the BGBCTP has had a significantly positive effect on the cognitive developments of the children in the experimental group. Besides the qualitative research findings revealed that the BGBCTP has a positive effect on children's linguistic, shape-space, reasoning, discrimination and numerical abilities. In conclusion, BGBCTP is an effective programme on the cognitive development of children.