My personal experience with private schools arent positive. Thus I wont recommend it.
The reality is, Private Schools are a commercial entity. Commercial means that they are out there solely to make money.
Instead of investing so much money on that, why not apply to the government subsidized institution for N, O and A level by ITE.
One subject is about 90 dollar and this will cover the months from April, all the way to October.
A link to the webpage is hereEdited to add that the teachers that are teaching for the Night Classes are aptly qualified - most being teachers and lecturers for local JCs, as opposed to popular perception.