Calculating rolling mean

I would like to calculate 6 point rolling means on a field after a query. A group of technical staff do 4 performance tests each month so one table records all results in a column/field of a table where the table has the date of test. So the field shows all staff results each month and all months in the same table. I need six point rolling average performance for each staff member. This needs to be produced against each result. I know of the Last function and the Max function but cannot work out how to do this--any ideas? I think I would start with a Group By on the staff member initials (this is what we put in rather than their names).