Sports attire.
If you are joining ballet for the first time and want to try some classes before comiting to buying all the proper attire then you may wear standard sporting gear until you are ready to commit.
This includes pants such as yoga pants or tights that are tight on the legs so that the teachers can see clearly the lines of your legs to help you achieve proper execution of the movements.
Sports tops are prefered over loosly fitting T-shirts similarly so that the teachers can see your posture and help you make suitable adjustments to dance development.
Socks are suitable for your first couple of classes, however, it is recpmmende that you prepare a pair of customary ballet soft shoes as soon as you are ready to commit to a training package.