It depends on why they are struggling. If it has to do with social issues then yes, changing could help. It gives them a fresh start. But if they are constantly getting into trouble, then most likely they will look for the same types of friends and trouble at a new school. It if is low grades then moving is a terrible idea. They will be trying to play catch up, learn what new teachers expect, and worrying about their social life. Middle school is a really hard time in a teens life, parents just need to be patient and present. Make sure they know you care and you will both make it through.