At Maths Conference 4 recently I attended a session on marking, Martin Noon’s “Marking for the Reluctant Marker”. you can find Martin’s resources from the session here.
The session was a reminder to me that I really wanted to try the RAG 123 idea, something I had already read about from Kev Lister.
I decided I wanted a very simple version without the word level anywhere and created my version as follows: Marking Guide (Word) Marking Guide (pdf). (We assess students on their “Engagement with Learning”, criteria they are familiar with.)

I also created a version for students to stick in their books for reference.
Student version RAG 123 student books (Word) RAG 123 student books (pdf)

Having tried this with my Year 9 class this week I am convinced this is something I want to try next academic year. Talking to a student later she said she thought it would be useful in other subjects too.
I explained the idea at the beginning of the lesson and let them know that I would ask them for their assessments at the end of the lesson, stressing that a 3 for understanding was a note to me that they needed help
Having collected the set of books it took a very short time to go through the set and see their I believe very honest RAG 123 assessment on the work on Functions we have been studying. I signed my agreement of their assessment. Some students also made additional comments to clarify / justify the reasons for their assessment.