Unfortunately now there are those who will never be able to drive because of their lack of academic ability.  This is very sad and again discriminatory, but for those would-be drivers there is no point in either raising their hopes or wasting their money if they are not going to succeed and so I would recommend they begin to learn the theory before they get deeply into the practical course, to see if they will be able to reach the required standard.  Further Education Colleges and Adult Literacy classes can sometimes offer help.