Children were said to have returned home in tears after seeing wildfowl shot and dogs retrieving their lifeless bodies.
Parents have now complained to Ashbeach Primary School in Ramsey St Mary's, Cambridgeshire, saying they thought their kids were going bird-watching at Welney Marshes, Norfolk, not to see ducks being shot at.
One dad, Ray Poolman, 49, told the Daily Mail that his horrified 10 year-old daughter was distraught after what she'd witnessed.
"She thought she was going to a bird-watching place but it turns out it was a shoot," he said.
A letter had been sent home by the school informing parents that the 22 children would watch a "flight", but Mr Poolman said it did not say children would witness birds being shot:
"I have since spoken to some of my friends who go shooting and they told me that 'flight' means 'shoot'. I thought the kids would be watching the birds coming into roost or migrating.
"My daughter came home absolutely distraught and in floods of tears. I was absolutely unaware that it was a shoot, otherwise she wouldn't have been there. There's no way it's an educational trip.
"It shouldn't have been arranged by teachers in school time. I can't believe they put children in that environment. What if something had gone wrong?"
Mr Poolman told the Mail he had met with Ashbeach headteacher, Shirley Stapleton after the trip last Wednesday, but that she had told him the trip was "rural and normal".
"Mrs Stapleton argued that we had agreed to it because we'd had a letter but it doesn't say they were going to take my child where they are shooting birds," Mr Poolman said.
"They allowed children to witness the death of an animal."
Mrs Stapleton defended the trip, telling the newspaper: "This is an annual trip which has taken place for several years.
"It is not compulsory - it is entirely up to individuals and parents must return a signed permission slip before their child can go.
"Following a class discussion about the visit, a letter was sent home to explain that children would find out more about wildfowling, the conservation of the landscape and the dogs and equipment used.
"The letter sent home before the trip made it clear that wildfowling was involved.
"The school does not promote the shooting of wildlife but tries to encourage children to be able to make informed decisions about the traditions, sports and activities which take place in their local environment.
"All the children indicated at the end of the visit that they had thoroughly enjoyed it.
"However, if any parents feel they were unclear about what the children would be experiencing, I would be very happy to talk to them."
Would you object to a school trip like this for your children?