Work his tail off on the ground for a while and get him to where he is actually paying attention to you (looking you in the eye, giving you his ears, etc.).
I think we often forget we have to, in a way, 'earn the right' to a horse's focus...if we don't actually work for it, how do we expect him to give it? So make him work hard for you for a few lessons...get to the barn early, and take him out, and ask your instructor if she has some groundwork exercises you can work on with him to establish respect and trust. I think you will see a drastic difference if you strive to gain his focus, rather than trying to ignore the fact that he is ignoring you and being a punk about wanting to be with his lady friend.
When you do get on, if you have to, work circles, figure eights, etc...straight lines are not usually conducive for showing a horse you are serious about wanting his focus...you have to move his feet; backwards, fowards, left and right.