Previous studies indicated that game elements may make players have joyful experience but some research indicated that players' learning performance may not be as good as what was expected. This might be due to the fact that poor user interface presented in serious games hindered students' learning performance. Therefore, designers should not only consider game elements, but also take into account interface elements. However, there is a lack of such studies that pay attention to both game elements and interface elements when developing serious games. To this end, this study aims to investigate how interface elements and game elements are considered in the design of serious games. A peer assessment approach is applied to achieve this aim. The results from the peer assessment indicated that designers generally tended to focus on game elements and paid less attention to interface elements. Furthermore, all game elements were similarly considered but interface elements were not equally treated. In particular, designers seemed to ignore the importance of error prevention and recovery from errors.