Is teacher a proper noun

No, the Word teacher is a common noun. The teacher's name would be the proper noun:

Our teacher, Ms. Campbell, gives too much homework.

A proper noun is the name of a person, place, thing, or a title; for example:

• Teacher Haven (store), Austin TX
• Teacher Road, Jamaica VT
• Teacher Insurance & Annuity, Charlotte NC
• 'Bad Teacher' (2011) with Cameron Diaz