Hafner Street in Newark is no more or less safe than any other area. No one can guarantee absolute safety for you. I recently listed a house on Hafner Street for owners who had lived there for several years before renting it out. The enjoyed their house before moving to a larger house. The tenants have been living there for over a year and stayed when the house changed hands. They also enjoy the area.
Here is a link to the Newark School site to determine the attendance area: http://nusd.ca.schoolloop.com/cms/page_view?d=x&piid=&vpid=1240064940878
Here is a link to the API scores for Newark schools: http://nusd.ca.schoolloop.com/cms/page_view?d=x&piid=&vpid=1232963806535
Both of these links are found on the website of the Newark Unified School District.... more