A common, logical technique in teaching is to invite students to highlight their gaps or errors by writing the correct answers or improvements in a different colour pen, to show them and their teacher which answers they got wrong and where they have made corrections. The idea is that this then supports further study and improves learning.
Quite often the colour is green (because red is for teachers or something?) – hence ‘green penning’. Amusingly enough, I’ve been to plenty of schools where they call it green penning, even if they don’t really care what colour is used. It’s just become the name of the corrections technique.
Teachers use this with all good intentions but, with my view from the back, I often see that the technique just doesn’t work at all for students with significant gaps in knowledge – ie lots of green pen – or where any particular correct answer doesn’t make any sense to them at all.
They go through the motions of writing down the correct answers in their green pen…. the teacher assumes this has been done successfully and that a knowledge gap has been addressed… but all that has happened is that the student has added to the list of things in their book that they don’t know or understand.