Varies. Sometimes patients will appear to have bad posture, but it can simply be there scoliosis, which is a spinal deformity. Other times patients can truly have bad posture that can worsen the appearance of their scoliosis. Doing some postural exercises or even physical therapy can at least help with the posture part of it. Xrays can give an idea about the size and flexibility of your curve. Thanks.
Don't worry. Poor posture does not cause scoliosis, scoliosis causes bad posture but most bad posture isn't from scoliosis. Have your teen see his pediatrician. If he does not have scoliosis then don't worry about it. Here is a little video on the scoliosis exam https://www.Youtube.Com/watch?V=yqzir6jja2u.