1-Create a lesson with Re-takes allowed set to Yes and Handling re-takes to "Use mean".
2-As a student, attempt the lesson twice, then verify that your grade is the mean of both attempts.
3-As a teacher, switch th Handling of re-takes to "Use maximum".
4-As the student who did the 2 attemps, the grad will still be the mean of the attempts.
5-As a new student, attempt the lesson twice.
6-The grade of the new student will be the best of both attempts, while the grade of the first student will still be the mean of his attempts.