Working memory capacity has been found to be impaired in adolescents with various psychological problems, such as addictive behaviors. Training of working memory capacity can lead to significant behavioral improvements, but it is usually long and tedious, taxing participants' motivation to train. This study aimed to evaluate whether adding game elements to the training could help improve adolescents' motivation to train while improving cognition. A total of 84 high school students were allocated to a working memory capacity training, a gamified working memory capacity training, or a placebo condition. Working memory capacity, motivation to train, and drinking habits were assessed before and after training. Self-reported evaluations did not show a self-reported preference for the game, but participants in the gamified working memory capacity training condition did train significantly longer. The game successfully increased motivation to train, but this effect faded over time. Working memory capacity increased equally in all conditions but did not lead to significantly lower drinking, which may be due to low drinking levels at baseline. We recommend that future studies attempt to prolong this motivational effect, as it appeared to fade over time. [Abstract copyright: ©Wouter J Boendermaker, Thomas E Gladwin, Margot Peeters, Pier JM Prins, Reinout W Wiers. Originally published in JMIR Serious Games (http://games.jmir.org), 23.05.2018.]