A head teacher says he is "sorry" if homework asking pupils to define types of hardcore pornography led them to undertake inappropriate web searches.
The work was given to children, aged 11 to 14, at Archbishop Sentamu Academy in Hull, the Hull Daily Mail reported.
Principal Chay Bell stressed the assignment did not require internet research as the answers were in the material the pupils were sent.
Leon Dagon was "flabbergasted" when he saw his 13-year-old sister's homework.
The work is part of pupils' Personal, Social and Health Education (PSHE) learning, the school said.
The students were asked to "define" topics including hardcore pornography, soft pornography as well as female genital mutilation and breast ironing.
They were also asked questions about alcohol, drugs and smoking, as part of the homework.
Mr Dagon, who took to Facebook to share his concerns, said: "My little sister knows make-up and TikTok at the age of 13. She doesn't know about hardcore porn, and then asking her to define it.
"The majority of children nowadays will now go on the internet to help them with their homework and if you type that kind of thing on the internet, God knows what's going to pop up."
Mr Bell said: "I am genuinely sorry if parents or students have unnecessarily researched any of these phrases and for any offence caused by this mistake."
He said students "were not directed to research these topics themselves on the internet because all the answers to the questions posed are contained in the teacher-produced materials we shared".
The work was in line with government guidance, but he added: "I have asked that no future PSHE materials contain any potentially sensitive content and will ensure all materials are fully age-appropriate."
A spokesman for the Department for Education said it was a matter for the school and had no further comment to make.