Do students have to belong to an org. group to access the collector app? I built a collection map and when my students tried to login with their account, they could not find the map.
Your map has to be shared with a Group that they are a member of, Share with Everyone wont get it.
Here is a worksheet on setting the Collector app up including creating the feature service in ArcGIS Online and creating a Group:
I hope that helps.
Retrieving data ...