It happens sometimes that students have to stop taking lessons and learning music for a while, yet they really want to carry on when they have an opportunity to do so again. Some of my students have had short breaks in learning, some others have had much longer breaks. In particular during and after lockdowns, some students had to stop taking private lessons because of financial constraints, whilst others just simply had too much going on to be able to carry on with lessons.
In either case, students would have a foundation on which to build later learning when they return to lessons. In my experience, there are great differences between students and how much they can remember and recall from their past lessons. Some students seem to have a very good memory for music theory and musical notation; others seem to be able to play songs easily, indicating that their muscle memory is strong. Very few have strong recollection in both!
This is where different learning styles become evident. Those with more visual way of learning seem to be more confident with music notation, whilst those with more aural learning style seem to be confident with the motor skills and learning pieces to play.
As a teacher, it is your responsibility to assess where the student is at when they come to you and to give your students tasks that are at appropriate level to them. Often, with students who have had a break in their learning, it is nice to restart lessons with something more relaxed and fun, such as songs that they might know. It is crucial to engage the student and help them feel motivated straight from the start. If students lose motivation, they are unlikely to want to carry on with learning music.
Once the lessons have started up again, it is then easier to give students more challenges and to accelerate their learning!