From your description, it sounds to me like there could be a few potential causes for your issue. The first possibility is that the Slingbox unit has not been completely set up for remote viewing. Your home router might be blocking the signal from reaching your son's location. If that is the case, the solution would be to port forward your router and the Slingbox. Since your unit is an M1, it is less likely that portforwarding would need to be completed manually, as the Slingbox setup process is usually pretty successful in doing that for customers automatically. Still, depending on your home network settings, it is certainly a possibility. That would absolutely explain why you are able to watch from the home location, and not remotely. Here are some additional resources to assist in resolving that problem, and you are welcome, of course, to contact our technical support department at 1-877-GO-SLING.
Another possible cause, and in my opinion, the most likely cause for your issue is that something at your son's end is preventing him from connecting to the unit. Are you able to connect remotely from other public networks? Or does it only work in your home? If you can connect remotely from other places, but not your son's college, then it is probably a security setting within their network. To resolve that, your son might need to reach out to the campus IT department to see if a firewall or security setting is disrupting the signal. I would also recommend uninstalling and reinstalling the application on the device he is attempting to view the Slingbox.