Android specifically supports campus IDs in the United States and Canada through Transact and CBORD. If your university doesn't partner with one of these companies, or you live elsewhere, you won't be able to add a student ID to Google Wallet — at least for now.
Transact claims that it "serves more than 12 million students across 1,750+ client institutions," while CBORD works with 900 campus partners. American and Canadian students have decent odds that their college employs the technology that backs Wallet IDs. But there isn't an official list anywhere: Instead, Google recommends that you "contact your campus card office" to find out for certain.