@One Eyed Mind,
Well, regarding body language: he tend to mimic my behaviour: if I laugh, he laughs, if I sit or stand up, he does the same, etc.
He also smiles a lot, looks to me profoundly in the eye, does lingering looks. Also, he asked me if I'm single or if I'm with someone, and asked me other personal questions as well. Why would he ask that if he wasn't interested, I guess!? For ex, I have a 5 year old son and he asked me if on weekends I'm always with him, or if I'm alone sometimes as well.
He also asks me a lot of general questions like what am I doing on the day of the lesson, if I'm going out, staying at home, etc., and general questions about what I like or don't like like sports, food, etc. We do seem to have a lot in common!
But I guess what strikes me the most it's the way he looks at me! His eyes tell it all really. And yes, I've noticed his eyes changing when he's looking to someone else.
So, this provides you with a bit more info?