As a fellow teacher can someone give advice on how I should convince a student that this is not correct:
I wondered if I should open the door
I wonder if I should open the door and I wondered if I should have opened the door. And maybe even the above phrase is possible if the person wondered "should I open the door". Which grammar points should I analyse for this explanation?
I don't see why you think it is wrong, though I would use 'whether'. If they didn't open the door and then questioned that decision, it would be 'should have', but if it's reporting the thought, then 'should open' is fine IMO.