Reformatory

In chapter 4 of Great Expectations, the term Reformatory has a specific 19th century meaning. 

A reformatory was an institution for young offenders, intended not merely to punish them but to reform their character and behaviour through discipline, education and work.  In chapter 4 of Dickens's Great Expectations, the author gives us a rather curious collection of people connected with the Christmas gathering.  Pip's idea of her sister's idea is that he was a young offender and needs some correction; and his birth is against the dictates of reason and religion; and his clothes were ordered to be made in the fashion of a reformatory inmates. 

In Dickens's time Britain had been developing institutions specifically for juvenile offenders.  So, Pip thinks that his sister has directed the tailors to design Pip's clothes in reformatory style.