Efficient coordination is a major source of efficiency gains. We study in an experimental coordination game with 727 children and teenagers, aged 9 to 18 years, the strategies played in pre-adulthood. In our one-shot, experimental coordination game, we vary the incentives for reaching the more efficient equilibrium and the number of subjects within a group. Looking at strategy choices dependent on age, we do not find robust age effects in the aggregate. Yet, we see that smaller group sizes and larger incentives increase the likelihood of choosing the efficient strategy. The larger strategic uncertainty in larger groups is obviously harmful for overall efficiency. Regarding incentives, we find that increasing the profits in the efficient equilibrium seems to work better than providing a cushion in case of miscoordination. Beliefs play an important role as well, as subjects are more likely to play the efficient strategy when they expect others to do so as well. Our results are robust to controlling for individual risk-, time-, and social preferences.