The celebration took place at Heavers Farm Primary School in South East London in June 2018 as part of gay pride month.
Despite questions from parents, the school allegedly said it did not come under sexual education and so opt-outs would not be granted, where they might have done in a lesson.
Head teacher Susan Papas defended the event back in the summer, in a statement to the Croydon Advertiser, she said: "We believe that it is important to teach children about diversity and acceptance. We have received many messages of support from parents for this.
"We stand by our decision to celebrate national Pride Month by teaching British values. We will continue to raise awareness of the diverse nature of our whole school community to ensure that everyone feels valued."
Fourteen parents are said to have complained to the school, with Izoduwa Adhedo, pictured above with her husband, attending a meeting with the school governors on Tuesday evening.
Roger Kiska from the Christian Legal Centre will be accompanying her, he told Premier: "She would have liked more consultation, she would have liked opt-outs".
Mrs Adhedo says that since she queried the school, staff have treated her differently: "After I complained about my young child being forced to take place in an event that goes against our Christian beliefs, the school's attitude towards me changed completely. I know other parents who are afraid to speak up because of how the school has treated me.
"It was like being bullied. They stopped treating me like any other parent but were antagonistic towards me. I believe that they retaliated against me by unreasonably excluding me from the premises, victimising my child and not taking my safeguarding concerns seriously."
Her son no longer attends the school because she feels they were 'bullied out of it'.
Mrs Adhedo is going back to Heavers Farm Primary School on Tuesday evening to raise these concerns about the behaviour of senior members of staff, saying they misled her with incorrect statements of law and failed to follow proper procedures.
Premier has contacted the school for a response to the latest allegations.
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