The following URLs are the ones you most likely want to whitelist:
- Main servers: http://ai2.appinventor.mit.edu/ and http://code.appinventor.mit.edu/
- Login server: http://login.appinventor.mit.edu
- Rendezvous (for establishing live testing connections): http://rendezvous.appinventor.mit.edu
If your teachers use CloudDB as part of their curriculum, you'll also need to whitelist connections to clouddb.appinventor.mit.edu on port 6381.
You may also want to take a look at: