How did Barack Obama's parents pay for private school?

When he was in Indonesia, at first his mother home-schooled him. Later, he attended a government run school, which did not seem to be expensive; by that time both his mom and step-father had good jobs. In Hawaii, after his mother became ill, Barack was raised by his maternal grandmother and grandfather: they were solidly middle to upper middle class, and in fact, his grandmother had a very good job, so they seem to have been able to afford to send him to a private school; on the other hand, he might have gotten some financial aid, which many private schools make available.