Teachers at a Wearside primary took to the picket lines in protest against academy conversion plans.
The members of the NASUWT at Highfield Community Primary School are thought to be the first in the North East from a single primary to take strike action in three decades.
The move follows concerns over proposals for their school to form an academy partnership trust with another primary in the city.
Supported by other union members, around 14 Highfield teachers, which is more than 80% of the teaching staff, at the Ford Estate school voted for the walk out and were outside the school with placards this morning.
There were also a number of other staff at the school who refused to cross the picket line.
The local authority said parents were being kept informed of the situation and the school remained open.
John Hall, national executive of the NASUWT, said members believe there is the potential to result in adverse management and working practices, job security and changes to pay and conditions of service if the move goes ahead.
“The teachers are concerned for their future health and wellbeing if the governing body goes ahead with its support of forming a partnership between Highfield Community Primary School and Valley Road Community Primary School as part of the Iris Trust.”
Mr Hall said his members do not believe the school needs to become an academy, but if the governing body are set on it, then they want it to find an alternative trust to join.
He said members started to raise concerns late last year, after Valley Road Primary School first became involved with Highfield, and there are currently more than 100 grievances being investigated.
Mr Hall said: "I have worked in this industry for 30 years and I have never come across teachers from a primary school striking on their own before.
"The strength of feeling is so high from our members that they do not want to form a partnership with Valley Road that they have voted to take this action."
Simon Kennedy, NASUWT regional organiser, said teachers feel the children at Highfield would not benefit at all by these plans and the two schools are not a good fit.
He said: "Nobody takes strike action lightly. There has been a big change in the staff morale at the school.
"Our members just want what is best for the school. If staff are unhappy then that is going to impact on the children."
Coun Louise Farthing, Sunderland City Council Portfolio Holder for Children’s Services, said: "The staff and governing bodies of both schools continue to work closely together, along with ourselves and Together for Children, to ensure that any decisions on the future of both schools are made with the best interests of their current and future pupils at heart."
If the issue is not resolved the NASUWT members at Highfield have further strike action planned for May 3, 4, 16, 17 and 18.