I have a student who has an amazing body, but has that "teenage troll" look about her. Meaning, her shoulders are constantly rolled forward and she looks slightly hunched over because of it. I feel I've provided every suggestion, visualization, physical correction that I know of in my 10 years of teaching. Nothing seems to work to get her to pull her shoulders back and bring her shoulder blades together. She seems to understand what she needs to do, and has even commented she's having a really hard time trying to correct her shoulders. We work on core exercises and she is pulling in her core while she dances. I've told her to not be afraid to stick those boobs out while dancing. She has only been able to perform this once, meaning pull her shoulders back and look like she's fully standing up straight. It doesn't seem to be coming from her lower back either, as in slouching or sitting into her pelvis where the spine meets it. I've threatened to somehow tape a yard stick across her shoulder blades so that she is forced to pull her shoulders back (only kidding, but secretly I'd love to do it!).

Curious what others' suggestions are.

X-posted in Irish section.

Have you tried working with her neck and shoulders? If she's sloping her shoulders forward, she's likely got a problem with her neck posture as well. The visual that really helped me correct this problem back in my younger days was to picture a string drawing me upward from the crown of my head. When you are lengthening your spine and aligning your head and neck properly, it's much easier to keep the shoulders in place as well.

I have this problem with a lot of my teenagers. I have them all face the mirror and shake their arms out and then let them hang by their side. I tell them that when they do that they should have their thumbs/side of the hand/"thumbpit" face the mirror not the back of their hand. If they have their shoulders back their arms will fall correctly. If they are slouching their hands will roll to show the back of the hand. Most of them have the back of their hands facing the mirror. Usually they get self concious because they can clearly see its wrong. For some reason thats easier to see than a slouched back. Plus they can clearly see who else around the room is right or wrong. I find it works because it also shifts the emphasis to the hand placement and it feel less like nagging about posture all the time. (of course I also nag about posture as well!) I like it too because they have to play with their back and shoulder muscles to figure out how to fix the hand placement. It tends to connect body parts for them.

I also play a game when I'm trying to fix a bad habit (not pointing feet, posture, raised shoulder,etc). If we are doing a routine we will start form the beginning with music. Everytime I notice the bad habit I stop the music and we start over. It tends to be frustrating but as long as you keep it light and fun the frustration will force them to work harder and be more aware because they get sick of starting over. Especially as they get further into the dance! I do this a lot with my younger students but it works on the older ones as well.

I use beanie babies on the head for my little ones to help with posture, maybe you could put them on her shoulders? If she hunched over they would fall forward. Have you pointed it out to the Mom also? If she's commented that she's having trouble with it it may be worth a Dr. visit just to be checked for scoliosis which can cause a hunching of the shoulders, or bad posture...

Yeah, mom knows about it (mom takes dance from me as well). There's nothing physically wrong with her like scoliosis. We do work on the string pulling you up through your head visual. I will try to emphasize more neck than shoulders, but as I'm sitting her trying that, I see that I can pull my neck and head up while still having my shoulder rolled in.

I do the beanbag on the head thing too, right the way from my first Ballet group to my teenagers, it makes them think about it, then we do demi plie's rises and tendus at the barre and then later on in the centre too, not every lesson, just now and again, or when they ask to do it. It treated as a bit of light relief by all of them as they really like to see who's going to drop the beanbag and who'll manage to keep it going.

It is not the shoulders that need to be pulled back. Tell her to lift her spine like someone is pulling her up by the top of her ears. It always works. Shoulders should be relaxed, as well as chest. The "lift" comes from the spine, starting from the top of the head.

There could be two reasons for the shoulder roll...
1. Emotional - Teenagers, whether they admit to us or not, seem to adopt this posture out of low self esteem, or self consciousness. This may or may not be the case with your dancer, but MANY postural faults come are far deeper stemming that simply physical.
2. Physical. It sounds like there is an imbalance between the front of her shoulder muscles (pecs) and the muscles between the shoulder blades (rhomboids) Specific exercises would help stretch out the front of the shoulders, and therefore lengthening the pecs (they are PULLING the shoulders forward) and the rhomboids are not string enough (and other back muscles of the thoraic region) to hold the shoulder blades DOWN. By sliding the shoudler blades down the back, corrects the roll forward of the shoulders. )
She may be very aware of this postural fault but simply does not have the muscle to hold it in place.
The exercises I am thinking of are Pilates based exercises, which called different things here (I am in Aust..) but if you are not familiar I would refer her to the physio. Hope this helps.

Have you tried a plumb line?

Sometimes a literal visual helps. I took profile pictures of my dancers standing in their 'best posture' next to a plumb line and when we reviewed the pictures they really started to understand how they looked and how to fix it!