When you create Formative Assessments, which receive grades and feedback, Moodle will automatically populate these grade items in the gradebook.

In order to remove them from the overall grade calculation:

• Create a Grade Category with the name: Not Counted Toward Final Grade
• Set the Category Weight to 0.00
• Place all assessments that do not contribute to the Final Grade under the new Grade Category, it doesn't matter what they are scored out of or what weights they are given.

Why does this work? 

The Course Total is a weighted mean of grades, just like the various Grade Categories that make up the Gradebook.

If you have three graded sections with weights that equal 100, plus a section weighted at 0, the total is still 100.

• Discussions = 40
• Assignments = 30
• Exams = 30
• Not Counted Toward Final Grade = 0
• TOTAL = 100

No matter what score a student receives underneath the 0.0 parent category, they are still just receiving a percentage of 0.0. Which is 0.0.