Whilst educational goals in recent years for mathematics education are foregrounded the development of mathematical competencies, little is known about mathematics teachers' competencies. In this study, a group of practising teachers were asked to solve an algebra problem, and their solutions were analysed to determine the competencies apparent (or, equally importantly, absent) in these solutions. The most demonstrated competencies were "devising strategies" and "mathematising," whilst "communication" and "reasoning" were mostly missed. The research provides a detailed methodology on how mathematical competencies can be assessed in the context of problem solving.