You are maybe not seeing a drop-down menu on the right side of the page. This happened to me once. Actually there are as many wikis as groups. There is no main page for the whole, and as teacher, you can get into all of them.
Hope it works,
I am having the same problem as Ana Garcia. The students presented their wikis but when I try to access the wikis there is nothing there, just the screen asking to create a new page...
You talked about a "drop-down menu on the right"... I do not see a drop-down menu. Can you be more specific? Where exactly is the drop-down menu located?