Tutors, working as individuals (not as members of a tutorial college), can provide one-to-one teaching to help children overcome their learning difficulties or prepare for an examination, including entrance exams to secondary schools, or with a particular subject eg languages or maths. Make sure you select one that is in touch with the exams for which your child is being prepared.
There is a professional body, the Association of Tutors, although not all good tutors are members. You can use its website to search for a suitable tutor (http://www.tutor.co.uk">www.tutor.co.uk, tel 01604 624 171).