It sounds like you should populate the exams field *after* the user selects the student name. To do so, you could use AJAX to send the student choice to server and have it query the exams and send them back. Alternatively, when you create the page, you could send a data table containing a cross reference of students vs exams, and use the event generated when the student is chosen to build the appropriate options into the drop-down box.

...roboticus

When your only tool is a hammer, all problems look like your thumb.