This kind of a plan sounds great, but is IMO close to untenable in the real world.
Build a great big school.
Out of what ? Sure, you can build the building itself. But you also need (among other things) electric power, a reliable food supply, clean water, medical care, computers, plus a ton of muscle to protect you from people who will want to take all of the previously mentioned stuff. Poor countries have none of that. Well, they might have some muscle, but reliable security is tough to buy.
Offer the following deal to parents of gifted children: they send their children to you, and you'll educate them for free, for ten years
You will be overwhelmed with offers in a matter of days. How do you decide which children are gifted ?
If at any point they do start working, you get (say) 10% of their income for 10 years.
How will you enforce that ? Actually, before you can enforce anything, where will your graduates find work ?
Obviously you still need some instructors.
Where will you get them ? Do your kids speak English ? Do your instructors ?
Do it morally
Trust me, this will be the least of your worries.
Generalizing about 'poor countries' like this annoys me.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.