Ideally if you are giving maths grinds you will have a mouse which you can use on the interactive whiteboard. A track pad on a laptop is quite difficult to use so in the case of using a laptop you should plug in a mouse or have prepared questions and answers for the student to work through. In this case it will require you to be extra prepared as it can be more difficult to communicate "mathsy" subjects via speech and documents.
Alternatively, if you would like to purchase a graphics tablet to take your grinds to the next level there are multiple options on Amazon.com which will seriously enhance your performance as a tutor.