I think the best investment a poor country can make in education is more effective teaching methods.
Investing in better technology can be an expensive trap, especially if corruption is and issue. It also requires teachers to be taught to use the technology properly.
By changing schools to a place where students are active in their own learning you can achieve wonders. Look at Finland as an example. 
This learning pyramid (from Advanced web banking.com) shows the difference in retention rates from 75% for hands on practice and 90% for teaching. That's why in my country Australia, students do a lot of projects and give presentations and tutorials.