With data from 311 K-12 public school teachers working in the United States, we tested a predictive model of entrepreneurial behaviour that included demographic characteristics and career adaptability, and identified differences between highly and minimally entrepreneurial teachers on how and why they adapt their teaching practices. Statistical analysis identified education and career adaptability to predict entrepreneurial behaviour. Qualitative analysis revealed that highly entrepreneurial teachers considered their professional development and the broader school system, while teachers scoring low on entrepreneurial behaviour focused on behaviour management and coping with imposed regulations when adapting their practices. The discussion includes theoretical and practical implications.