It's not just the girls that get this effect, when the guy who is junior to me in our class started, he was gawky, uncoordinated and looked scared of his shadow. Now after learning for 4 months, he's looking so much more confident and he's filled out his stature, he looks like he's put on body shape, a lot of it is the way he carries himself but doing TKD has given him some core strength too, he's now self confident and no longer looks like someone who's bullied a lot, he looks like the guy you don't mess with. All after 4 months training and a little encouragement.
Good for him! I love hearing things like that! It works the other way too, our best pro MMA fighter is 19 now but his mum brought him to us when he was 13 and being a real pain in the butt, thought he was hard and was getting in with the wrong people. he got knocked around a bit because he went in thinking he knew everything, He stuck it out though and is now a pro fighter who is quite, confident and mature! He teaches the children who adore him and he is respected and listen to by the adults including some of the best fighters in the country. Currently he's a British title holder and ranked 2nd at his weight. We are very proud of him ( and his mum is very relieved!)
http://www.mmauniverse.com/fighters/SS14964 (this isn't up to date though)