Can't enroll in other courses?

i finished the hunter-gatherer and the messenger course at the thakrian school but it wont let me join the school militia and the fourth course donst seem to exist (i only see the three classrooms + the eatery)

The militia school is broken for all cities. I think the original intent is to have the scholars throughout Avalon fight each other for it, but First Age simply doesn't have a sufficient player base to justify it.

The missing course you're talking about is the disciple course, and it really is there, but it's probably in a strange direction. Check up and down, failing that, check in and out.

if you have completed two course then normally you should be able to graduate. The disciple course is there to complete but I dont think it is required.

Thorongil is correct, you only need to complete 2 of the 4 courses to graduate.

Zalastra is also correct, the militia course is disabled in First Age because there aren't enough new players to justify having it (unfortunate, because its probably the most useful course).

Most people choose to do the Messenger course and the Hunter/Gatherer course because they are the easiest; however you can choose to do disciple as an extra or in place of one of the others.

Once you have declared success in the classes, you should be able to type ATTEMPT GRADUATION or GRADUATE... something along those lines... and if you have met the requirements, you will be declared a graduate of the city school and be able to choose your guild and start your adventures in Avalon.