ANSWER: The teachers make it clear which of the notes should be included. They usually say these sentences:
1. "Here's what you should remember" - This indicates that it should be included in the notes and is important.
2. "This is important" - This is a direct statement that is it important and may come in an examination. It also indicates that this notes may have been useful in the past exams.
3. "Include this in your notes" - Here the teacher is directly instructing the student to include it in the notes as it is very important for him/her.