I think, a Teacher is the one who shows you the reality , who make you aware from the practicality of life and teaches you all social norms and give you knowledge whatever is there to understand for a proper living and make you stand by own for a decent living but a Guru works on deeper level.. They make you aware from themselves, from the universe, from the infinity. Like our very own Guru Mantra says
We all are made up of brahma,vishnu, shiva acc to hindu scriptures -- and we refer them as our gurus -- the ultimate ones -- the ones which are within ourselves, they will not make you grow as human but there will be spirituality growth. They will lead you to ultimate truth. It will make you see through which is beyond our logical minds and intellect and tell to surrender within this vibration.