In this paper we assess pre-service primary school teachers’ knowledge in relation to fair games. Common knowledge of content is assessed through the responses given by 167 preservice primary school teachers to two open-problems. In addition, two components of didactic knowledge are inferred trough the participants analyses, when working in small groups: (a) Specialized knowledge of content is assessed from their analyses of the tasks’ mathematical content; and (b) knowledge of content and students is assessed from their assessment of responses provided by primary school students. Results suggest the need to reinforce the training of pre-service teachers both in the mathematical and the didactic knowledge.