I have seen students blossom once they have the chance to sit quietly with a tutor one-on-one and listen to an explanation of the concept being studied. Once they get that little extra explanation and attention, and once they realize how important their success is to themselves, their teachers, their parents, and their tutor, they begin to view their subject matter in a new light. It gives them a foothold, something they were missing previously.
It is also extremely beneficial to bring a topic down to its basic level and build it up in front of the student to the level they might be studying in their school classes. Also, repetition is not harmful, but very helpful, to students who may be struggling. Subjects such as algebra and geometry can be very intimidating to students if they lack certain foundations.
Coming to tutoring helps them build those foundations and the structures that must arise from those foundations, step by step. Never be afraid to repeat. Never be slow to demonstrate. Never hold back on showing examples to the student. In this way, the student will experience one "Aha!" moment after another in their growth in the subject matter.