Of course parents are a child's first teacher: of language, behaviour, attitude and values.
Nurseries and schools have a role in ensuring good of language, behaviour, attitude and values . Usually that is just reinforcing what has already been instilled by the majority of good enough parents.
Occasionally there are parents who are overwhelmed by physical or mental illness, caring for others, unemployment and/or poor housing, parents who have poor levels of cognitive / educational development and of course there are just bad parents, too concerned with their own interests to worry about how their child is developing. These are not that common though!
Well that is my experience anyway!