This paper describes the design of Undersea Adventure (UA), a novel computer game to assess students’ collaborative skills development. UA is an innovative product that integrates theory-driven content with customized game mechanics. Game assessment approach facilitates covert assessment, enabling real-time collection of dynamic evidence of social skills, while players’ choices during gameplay yield essential data. To develop an engaging and valid game, we used an iterative data-driven validation process. This included creating, testing, and revising UA based on student performance and feedback, and retesting UA until gameplay aligned with independent ratings of collaborative skills. We first investigated the potential for utilizing detailed student behavior logs to enhance assessment accuracy. Our findings demonstrate that integrating external metrics assessing players’ collaboration skills with comprehensive behavioral logs pertaining to collaboration can effectively enhance the precision of built-in assessments. Next, we investigated the effectiveness of UA as a collaborative skills assessment tool. The assessment of the game demonstrated high levels of student engagement and favorability, as well as ensuring the reliability of data collection and analysis. These findings support the use of the interactive and engaging computer game format for the stealth assessment of students’ collaborative skills. The innovative design methodologies developed are expected to be advantageous in the improvement and refinement of educational computer games.