A modern instance of banning a language from schooling

No. The banning of a local language or dialect always aim at suppressing a minority - with the long-term aim of eliminating it altogether. First, you take away their local economy - seize and regulate whatever wealth there might be in the region; then you take away autonomy in any form of self-governance; then you take away their culture (forbid festivals, public ceremonies, religious observances and rituals, etc.; introduce aspects of the dominant culture in its place) ) then you take away their language - and with it their oral history.

The "larger nation" will benefit politically in the short term, if the regional minority becomes more productive and less troublesome.
In the long term, it loses diversity, colour, depth, traditional knowledge and skills, adaptability.
The minority nation or tribe may retain the lives of some hotheads that would otherwise have been shot down in rebellion, but the same, or even more, lives will be wasted in suicide, depression, obesity, substance abuse - all the ills of identity-loss.