Moodle allows you to provide quiz grades in the following ways:

1. Highest
2. Average
3. First
4. Last

However, my colleagues and I would like to provide a Moving Average that is based on our students last five attempts.

We would like this format to motivate our students to continue to attempt our randomized quizzes until they reach a certain grade.  We believe that the Average grade is less motivational when students trend their achievement.