As a teacher, I’ve found that sometimes it can be difficult to assign a new piece to students. Whether you’re teaching beginner, intermediate, or advanced students, you want to balance the new piece with new and existing techniques. If you assign a new piece of music that has only new techniques, then the student might not feel successful at the end of each lesson.
Usually I would do my research and see if the piece I’m thinking about will suit the student’s strengths while introducing some new ideas about the violin. These may include vibrato, shifting above first position, or new bow strokes.
You may also consider the date of the next performance when assigning your student their next piece. I find that there is a phase that is typically good for revisiting scales, etudes, and other technical studies.
All in all, teachers know their students best. Have a conversation with your student to see if they have anything they’d like to learn!