Yes you do have to do the prerequisite...
What is it about students wanting to take a course for which not only don't they have the prerequisite, they don't even have the prerequisite to the prerequisite?
Student T tried to enrol late on a particular advanced programming course (late enrolling students can be refused entry). Noticing that not only has he not passed the prerequisite programming course, he hasn't even passed the prerequisite for the prerequisite, I refused him entry. Next thing I know, he's made the same request again, this time accompanied by a wheedling email saying he does have a bit of programming experience and won't let me down. He says he'd talked to his adviser of studies, and his adviser was ok with it.
Hmm, what do I smell? The smell of unentitlement, betrayed by the "But my adviser said it would be ok...." prefix. I check T's record again. His record reveals that not only is there no evidence that he can program, but there is definite evidence to suggest he can't program, because he took the easiest programming course twice and failed it both times!
As for the adviser, no he had not ok-ed it and was perfectly happy that I refuse the student entry on a course for which he had not got the prerequisites. Why do students try and play us off against each other? Do they think we don't talk to each other?
Another student N, had tried the advanced programming course before, when he'd attempted to plagiarise his way through it, and then failed. Surprise. He tried to enrol again for the course, but this time he tried to enrol late. So I check his record and find out he hasn't got the prerequisite programming course, nor the prerequisite of the prerequisite (in other words he hasn't passed either of the two easier programming courses he needs in order to do the advanced course). So I reject the request, politely and carefully outlining why he isn't being enrolled, and suggesting he go and enrol for a basic programming module instead.
A few days later, along comes N with a form for me to sign to enrol him on the advanced programming course. He looked utterly astonished when I refused to sign it.