Most of schools or hi-schools don't have their own blackboards. That's my guess. Since they don't have any blackboards, they would be able to use blogs as blackboards; to discuss about topics or share thoughts.
Also, all school works can be added on blog and reviewed by students. If they want to come back and check on their homeworks, they can do through blog. There's less chance to miss homeworks.
It's more interesting and more exciting for kids to do things through computers instead of papers. Teachers might get more attention this way. Also, most of modern kids have more skill on typing, not writing.
