Propositional teacher knowledge is recognised as valuable in classroom teaching practice, yet little attention has been paid to it relative to practical knowledge. This mixed-methods study aimed to understand the relationship between teachers' propositional knowledge and their classroom teaching practice in the collaborative school context using the case of Chinese (Shanghai) novice secondary mathematics teachers. The first quantitative phase, analysing 95 teachers from the 2018 TALIS, finds that propositional Mathematics Pedagogical Content Knowledge (MPCK), General Pedagogy Knowledge (GPK) and Cross-curricular Teaching Knowledge (CTK) positively relate to effective teaching practice. The qualitative follow-up phase, interviewing six teachers with secondary mathematics teaching experience, suggests the value of propositional knowledge in three other areas, including Mathematical Content Knowledge (MCK), Curriculum Knowledge (CK), and Technological Pedagogical Content Knowledge (TPCK), as well as possible barriers in transforming propositional knowledge into practical knowledge. Overall results suggest that a collaborative school context aids this transition, helping teachers develop their practical knowledge to enhance the effectiveness of their teaching.