Has your teacher ever got you mixed up with someone else? Well, imagine the challenge they must face at this school.
Netherthorpe School, near Chesterfield in Derbyshire, has nine sets of twins - and they're all in year seven!
Staff there think it's so twin-credible that they're looking to see if they've broken a new record for the most sets of twins in one year.
Seeing double has made the teachers so confused that they've had to put some of them in different classes.
Hayley went along to meet them and find out what's good, as well as what's bad, about being a twin.