My coworker earns more than me, but we have the same job. What do I do ?

I have been working at a Preschool for a year and half. I am the head teacher in the class. I have 9 years experience and getting my degree. I went to my boss's office to put paperwork away and on a sticky note was all of the salaries of all the teachers. ( The new teacher we hired is making the most money) she has no experience and only basic units. I was asked to train her. I talked to my boss about it who in return said, " new hires just get a hire wage", i know its not fair but that's kinda how it is". I have 14 kids each day ( ratio is 12 kids to 1 teacher.) The co worker only has 2 to 3 kids everyday. I am very upset and want to know what i should do.