My grandad was one of the original pupil teachers. The bright students went to school two hours early to learn the day’s lessons. These children then taught the lessons, whilst the teacher sat at the front and kept discipline. Later in life he became a headmaster and was high up in the Scottish Masons.
He had specialised in maths teaching. I was no good at maths, so I had to interrupt the beach holidays of my school years to go for a couple of hours tutoring with my grandfather! (LCM -Lowest common Multiple….HCF -highest common factor! What the heck does that mean??).