A seven-year-old primary pupil took a BB gun into their school - leading to a warning that parents should not buy the realistic-looking weapons for their children.
Officers from Nottinghamshire Police said while the gun only took small pellets, it could easily have been perceived as a real firearm.
Writing on the Berridge Police Facebook page, the force said the gun looked "very convincing".
Officers added: "Under different circumstances, it could have been perceived to be a real firearm.
"The worst outcome would be that a child might end up looking down the barrel of a very real police firearm, and we would like to ensure that does not happen.
"We would like to urge parents in the strongest possible terms that not only does this have no place in a school, it shouldn't be in the possession of a seven year old.
"Furthermore, what need is there for anyone to have one at all?"
The Berridge area covers the Forest Fields, New Basford and Sherwood Rise parts of the city, and the school has not been named by police.