Learning accents is a task best supported by trained vocal coaches, but as a drama teacher there are methods that can be used in the classroom.
I have long been a fan of the fine vocal technique books by the likes of Patsy Rosenburg. More recently the BBC and British Library have provided recordings which I've used to examine different voices and define the specific features of accents.
A new app has now appeared which helps support the learning of accents. I was particularly impressed with this easy to follow guide to learning accents:
http://www.ideastap.com/ideasmag/the-knowledge/catherine-weate-how-to-do-accents
