I think probably a single nested recordset with a nested select statement inside it would probably be appropriate.
SELECT Count(*) AS ClassDays, (SELECT Count(*) FROM ozadmain WHERE studentID = nestidparam AND Absent = 1) AS CassAbsent FROM ozadmain WHERE studentID = mainidparam
Nest that inside a repeated region and set both nestidparam and mainidparam to run-time values of $_GET['studentID']
Just before the recordset add code that sets the value of $_GET['studentID'] to the repeated recordset value like:
$_GET['studentID'] = $_row_RepeatedRS['StudentID'];
Then you can do the math on the page to show the % with php.