when started at an early age it could motivate the child to do well and in the process/long run -this is the important part- get him/her into the habit of studying later on. such that the monetary/material reward is no longer that important but the personal satisfaction of one's achievement and eventually grew up an achiever. no corruption there.
but rewards system, like cash rewards for policemen, it's always a hit and miss. it motivates and at the same time breeds....corruption.