There are a couple of very good international NGOs that you might want to support--Room To Read (www.roomtoread.org) builds libraries and supports schools in Cambodia and Laos (and perhaps also in VN? Not sure.). They're a cool organization and have the infrastructure to distribute things to needy communities.

Also really good is the Asia Foundation's Books For Asia program, which is specifically dedicated to donating English and local-language books to needy schools all over Asia. asiafoundation.org/program/...-for-asia

That may be a little less direct than you're looking for, but these organizations might also be able to give you info about some specific schools, too. Great idea, and have a great trip!