The aim of this study was to examine the impact of assessing students' achievements in a physics course in the form of a group board game. Research was conducted in two groups of 131 high school students in Poland. In each school, the research sample was divided into experimental and control groups. Each group was taught by the same teacher and participated in the same courses and tests before the game. Just after finishing the course on waves and vibrations (school 1) and optics (school 2), experimental groups took part in a group board game to assess their knowledge. One week after the game, the experimental and control groups (not involved in the game) took part in the post-tests. Students from the experimental groups performed better in the game than in the tests given before the game. As well their results in the post-tests were significantly higher statistically than students from the control groups. Simultaneously, student's opinions in the experimental groups about the board game as an assessment method were collected in an open-descriptive form and in a short questionnaire, and analyzed. Results showed that students experienced a positive attitude toward the assessment method, a reduction of test anxiety and an increase in their motivation for learning.