what percentage of children finish school early because they are in developing countries?

Question

africa, poor countries,

Answer 1

Whilst not a complete answer, you'll get some indications in this UNESCO publication.
http://unesdoc.unesco.org/images/0014/001405/140540e.pdf

If you hunt around the UNESCO site, you are sure to find ,more pertinent data.
http://portal.unesco.org/education/en/ev.php-URL_ID=48712&URL_DO=DO_TOPIC&URL_SECTION=201.html

I hope this is useful.