I'm not sure what max or min date you are trying to retrieve. If you use the SQL statement without the max and min:
FROM perfgroups1to4 INNER JOIN oxadmain ON perfgroups1to4.studid=oxadmain.stuid
GROUP BY studid
ORDER BY name ASC
Whatever the first and last date in that query is will be returned as the max and min date when you add those references. You must be using the wrong query to begin with, because MAX and MIN will do what they are supposed to.
Get the query without the MAX and MIN working first, then you can use MAX and MIN to get the highest and lowest value from a particular field.
If you need help writing the SQL statement, that is something I can do in a premier support ticket.