How to sort aggregate rows

[AmitTheJsWhisperer]

Yo yo,

when my table is grouped i want to sort the aggregated rows.
so for example, a table with three columns (student school ,student name, student grade).
when the table is grouped by school i can sort the grades but the sort is in the lower level - sort each school's grades, i want the sort to be implemented also on the aggregated rows so each school will be sorted by it's students average grade and in each school will be sorted with in it's students.