Introduction Many students struggle with introductory algebra and teachers have little to guide them to assist their students learn this important component of mathematics. The project on teaching algebra conceptually (TAC) was designed to explore and create teaching approaches to assist students in Years 9 and 10 to develop a conceptual understanding of algebra. The effect of these teaching approaches was documented by use of a diagnostic tool that assessed and made students’ knowledge and strategic thinking in algebra explicit. Key findings Achievement in algebra can be enhanced by taking a structural perspective that provides high quality diagnostic assessment information to teachers. Effective teaching approaches that have an effect on student