Abstract. Educational video games have been employed by teachers in order to make educational software more attractive to students. However, limited research has been made on the design and assessment of the storytelling elements and the educational effectiveness of these games in sciences curricula. For this purpose, we used Scratch to develop a storytelling mathematics video game and then we measured its educational effect to a small group of twelve students. We found that the story-based math video game has captivated the interest of students and it has been beneficial in the improvement of their performance in an assessment test. Most notably, the improvement was higher for students who used to have poor performance in mathematics. In practice, educators should develop similar games for similar science topics (e.g., physics, chemistry, etc), while further research should consider the active involvement of students in the design of serious games.