I think efforts like this are probably very rewarding and draw good attention, but ultimately the change needs to happen more systemically.
In my mind there are serious barriers to systemic change in a place like a rural village in Tanzania. In many ways the place is systemically stuck in a state of stagnation due largely to outside forces that the people there cannot control.
My thought is that by providing education to the kids, you can give them the ability to assess and change their environment in a way that they otherwise couldn't. I think that will lead to positive change.
And since they are one day planning to help, they must maximize wealth in the interim. Obviously this wealth maximization can take unorthodox paths because ends justify the means.
Practically I believe the individual outcome will be of two kinds: a student will use their schooling to help their village, start a business and bring a small amount of improvement. Or they will leave the area and find work elsewhere. Neither is unsustainable. The worst outcome would be if everyone leaves and the village dies out. Could that happen? Maybe. But I think it is unlikely. Or at least, I think that education is unlikely going to be a major factor, because even without education people from villages move to cities to seek their fortune.
And while this is pure speculation, I'd like to believe that people with education are more likely to stay because thanks to ubiquitous internet they have more opportunities to use that education to their advantage even from their remote location.
Systematic change will happen when more people with better education move into the ranks of government or business where they can affect such change.
Btw: when I talk about education I don't just mean STEM. I also mean ethics or moral education to teach people that contributing to society is important. Sponsoring students does not achieve that on its own, but it's something others are working on, and these students tend to be grateful for the help they get that they also get the message in a way and are motivated to pay it forward.