To assess the cognitive level of player ability is difficult; many instruments are potentially biased, unreliable, and invalid test. Whereas, in serious game is important to know the cognitive level. If the cognitive level can be measured well, the mastery learning can be achieved. Mastery learning is the core of the learning process in serious game. To classify the cognitive level of players, researchers propose a cognitive skill game (CSG). CSG improves this cognitive concept to monitor how players interact with the game. This game employs learning vector quantization (LVQ) for optimization the cognitive skill input classification of the player. Training data in LVQ use data observation from the teacher. populations of cognitive skill classification in this research are pupils when playing the game. Mostly players cognitive skill game have cognitive skill category are trial and error. Some of them have expert category, and a few included in the group carefully. Thus the general level of skill of the player is still low.