I would avoid contact of any kind with the dog - do not look at it, say anything to it or think about it!!!! Be as slow and confident as you can be - there is no dog, there is no dog. As soon as it moves towards you stand still, cross your arms and look up. Ask your teacher to take the dog away!

This is a totally unacceptable situation for somebody in a teaching position to put you or other students in. I would be very assertive with the teacher. Say how much you love the lessons but feel unsafe and have already been injured several times. As well as yourself you have seen the dog bite another student. Tell her/him that the law does not look kindly on dogs that bite and she is risking prosecution and the life of the dog by continuing this way.

If the situation is not resolved you really should find another teacher and consider reporting the situation to the relevant authorities, you could be saving someone from serious injury.