The incident occurred when the class was being hosted last week by a sports club in Plymouth, Devon, and suddenly, the young participants were exposed to the "extremely distressing" material.
The NSPCC children's charity told the media there was a worrying pattern of meetings held on Zoom being "bombed" with images of child sexual abuse.
"Zoom strongly condemns such behaviour and appreciates the NSPCC's efforts to raise awareness around how best to prevent these kinds of attacks," the video conferencing platform said in a statement.
According to local police, the hacker which was yet to be identified gained access after the Zoom call's details were published on online forums.
Zoom said it has enabled meeting passwords and virtual waiting rooms by default for users enrolled in its primary and secondary school programe, as well Free Basic and Single Pro users.
"For users enrolled in our primary and secondary school programme, we have also updated the default screen share settings to ensure teachers are the only ones who can share content in class," said the company.
According to The Guardian, Other Zoom meetings that have been targeted with similar zoombombing include a wine-tasting event in Manchester that left some participants in tears.
Last month, the US Federal Bureau of Investigation (FBI) warned people about porn material being popped up during the Zoom video meetings.