Code:
method 1:
<cfquery datasource="training">
UPDATE SIGNUPTEST
SET Attended = #Form.Attended#
WHERE Auto = #Form.Auto#
</cfquery>
If, as I think you said, there's a whole list of checkboxes on this page, this won't work. You need to give each checkbox an identifier in the form, like "Attended_student_id", and then "SET Attended=Form.Attended_student_id WHERE student_id=form.student_id and Auto=form.Auto". The way you're doing it above would set only 1 value per class, unless i'm totally misunderstanding. If you're trying to set the attended value per student, per class, you can't just have one key, unless Auto represents "student x in class y".
Code:
method 2:
<CFQUERY NAME="Update" DATASOURCE="training">
<CFLOOP list="#Auto#" index="Auto">
UPDATE SIGNUPTEST (Auto,Attended)
VALUES (#Form.Auto#, #Form.Attended#)
</CFLOOP>
</CFQUERY>
Same with the above - you're looping over the class and updating 1 "Attended" value.