That's a great idea, though as you think of an App,you need to ask yourself...
1. How many children in school have access to a smart phone?
2. Is internet available for them to use the App and it's content?
3. Who is going to provide the content you need in the App? Teachers partnerships? How are you reaching out to them?
4. Will the content in the App be for self study? Or it will need someone to teach it to the students?
There are a number of questions.
I would suggest you start small, if you know the problem, how can you solve it without money or very little money for the Start?, Print outs? Trainings in holiday times?
As you walk towards the App, start small somewhere.