No homegroup detected

Have you checked to see if while at school, he changed his network visibility settings?

Does his computer see your home network as a "Home" network and not a "Public" network?

Open "Network and sharing center"

1. Verify if your network is a "Home" network. If so then:

Click "Change advanced sharing settings"
Expand the "Home and Work" setting.
Verify that "Network discovery" is turned on.
Verify that "Allow Windows to manage homegroup" option is selected.

2. If your network is seen as a public network, and it is actually your own network at home, then change it to be set as a "Home" network.

Back at the Network and sharing center you should see the name of your home network with an icon of either a bench for public, an building for work or a house for home network. if it is not a home network, click on the link below the name of the network and you can change it.