Research on learning through serious games has been gaining importance in recent years. We develop the serious game "Tempoly," concerning the learning of the four arithmetic operations on polynomials. A quasi-experimental study was carried out with 95 students of 8th grade, to evaluate the reactions of the students to the game, the effects of the use of the game in the students' learning, and the use of the game through time. According to data collected through a questionnaire, we may conclude that students liked to play the game, considered that the game helped them learning the polynomial operations and that what they learned in class was useful to play the game. It was concluded that students who played the game simultaneously with the classes improved their results in a pre/post-test more than the students who did not play the game and through a Mann-Whitney test, the results showed statistical differences. The study revealed that the students that had more time to play the game did play more out of the class.