The Serious ‘Slow’ Game Jam (SSGJ) is a new model for use in serious game design and research. Game jams contribute to creative, innovative and collaborative design, however, game jams for serious purposes require an alternative model that integrates domain experts within the jammer community to ensure the validity of their designs and content. Furthermore, a rigorous yet accessible design methodology is required to balance pedagogic and game aspects to support jammers, as well as to assist researchers in subsequent analysis and evaluation. A standard entertainment game jam model does not afford support for these aspects. The SSGJ model addresses these needs through an inclusive, collaborative, and creative framework for multidisciplinary teams, which includes: encouraging reflection and knowledge exchange; improving content validity; and providing continuous support and mentoring to participants. Reflection on the model highlights the importance of framing serious game jams as explicitly educational activities and embedding them into existing training contexts. The SSGJ model contributes to a collaborative serious game design methodology for the wider research community, irrespective of application domains.