This article begins with a historical overview of the STEM education policy and related classroom practices in Hong Kong. Against the backdrop that the Hong Kong education authority has been promoting STEM education over the past few years, there has been a pressing need for effective strategies of implementing STEM education in the context of reduced class size classrooms (i.e. small class teaching). With a view to addressing this need, this article strives to exemplify the incorporation of STEM education into small class teaching settings. Intended as a conceptual paper drawing on design approaches for STEM lessons and a small class teaching framework, the article demonstrates the relevance of STEM education to small class teaching. Two illustrative lesson design examples are provided to showcase how the design approaches and framework can be operationalised. In addition, the article also offers a thoughtful discussion concerning the potential challenges of delivering the two sample lessons as well as the coping strategies. It contributes to understanding of STEM education theories and provides a valuable reference for educational practitioners.