This document describes the #RAG123 marking system created by Kev Lister. It involves rating student work with a color (Red, Amber, Green) for effort and a number (1, 2, 3) for understanding after each lesson. This takes 5-15 minutes and provides timely feedback. It allows teachers to identify student progress, plan future lessons, and engage students in self-assessment and dialogue. Research shows schools using #RAG123 see improved student outcomes compared to control groups. The system provides benefits with no reported increase in workload.