Recommended Reading
Having taught large classes of 30 or more students and teaching in a pupil refferal unit has proven to me that it is impossible for a teacher to reach every person in a maths lesson in school. This leaves at least 1 student confused each lesson. If this escalates, that child loses confidence and then has gaps in their knowledge and may start to believe they 'can't do maths'.
A tutor can fill in those gaps and bring back confidence.
