If you're combining two fields before export, then it sounds like you need a calculated field added in your filemaker table that you can group by.
That could be as easy as a calculation of:
yourTable::preceptor number & yourTable::students name
Then you would group on that field instead of the preceptor number you're currently using.
I was really looking for a way to combine duplicate entries with unique data, where the preceptor number could be repeated in each record but the student name would be unique. So several records with different student names with the same preceptor. I found a long way to do this in excel, I was just hoping Filemaker could do this before the export.
As I noted, it can, you just need to create a new simple field that combines both of your indicators that make something "unique".