add the marks column to the database default blank/fail
enable it with a query that enumerates the same output as the prior attendance query and asks you to update the mark fields, for each row in the result array
can be all records or single records

if a student can only attend 1 course, add the column to the student table
if the student can attend more than one course create a table
marks (id,student_id,course_id,mark)

you already have a query that prints a list of the students able to take the exams
ingonring the bad code for the moment (really bad code)
and the poor field names
output a table in a form something like

php Syntax (Toggle Plain Text)

<?php echo '<table>';
for each $output ++{echo "<tr><td>$lastname</td><td>$firstname</td><td>$coursename</td><td><input 'name='mark' value='$mark'></td></tr>"; }
echo "</table><input type='submit'value='update marks'></form>"; }

<?php echo '<table>'; for each $output ++{echo "<tr><td>$lastname</td><td>$firstname</td><td>$coursename</td><td><input 'name='mark' value='$mark'></td></tr>"; } echo "</table><input type='submit'value='update marks'></form>"; }

and have the form submit to a script(or self) to update table marks with the marks data
it is a thought exercise this code does not work