There is a feature specific for this purpose of correctly projecting enrollment by grade.  

When you mark the "Duplicate" next to the second account for the split account students, it will remove the second listing from your enrollment reports.  It will only remove this from your enrollment reports but it will not remove them from your billing reports.  

This allows for grade based billing to be reported correctly when running reports as well as removing the need for a different grade category.   

To mark a student as duplicate: 

1. Go to the account you want to mark the student as duplicate.  Under More Options, select Update Parent and Student Information.
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2. Click on the box that says Mark as Duplicate.  It is always defaulted to "Off" but by clicking on it, it will turn to a green "On". 

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