The study evaluates the linear number board game "100 House." Taking into account Krajewski's (2003, 2013) development model of mathematical competencies, this game supports the development of mathematical competencies in 6-year-old children. The board game design is based on the American cognitive alignment framework approach and aims to enhance the number board game "Race to Space" (Laski & Siegler, 2014). German 6-year-old children (N = 48) received four game-playing sessions, either counting on from their current position on the board game (count-on condition) or counting their steps from one (count-from-1 condition). In a pretest, posttest, and follow-up session, children's mathematical performance was assessed. The results show that playing the game led to stable improvements, especially in mathematical competencies of the first and second level of the underlying development model. Children in the count-on condition displayed a greater benefit. Supporting mathematical competencies by playing number board games is discussed.