An 11-year-old boy has been separated from his classmates, because his hair - which he had cut so his sea cadet beret would fit - is considered to be too short.
Ben Anderson has been punished less than a month after starting at secondary school because his hair cut with the sides shaved to a very short grade of 0.5 is in breach of school policy.
Mum Steph Anderson has now threatened to pull her son out of Tor Bridge High School in Plymouth, Devon.
She said: "I got a phone call from the school to say that he would be sitting in segregation outside the office, including every break and lunch time until his hair grows."
Anderson added: "[Ben] got his hair cut on Monday night because he is the leading cadet in his squadron at sea cadets and he had to have his hair tidied up for inspection.
"He has to have it that short because his hair grows really quickly. It's not an offensive haircut.
"Where do his human rights come in when the school is telling him how long or short he can have his hair?
"He goes into school, abides by all the school uniform, is smart and tidy and is enthusiastic to learn and now he's sat in segregation as if he is naughty."
The school said its policy, signed by the parents or guardians of each pupil, states that haircuts must be no shorter than grade two. The rule is also stated in the uniform section on the school's website.
Miss Anderson insists she did not see the rule in the school's policy.
She said: "It's not fair; he shouldn't be punished for something we didn't know anything about.
"If I had known, I might not have chosen the school."
Liz Dunstan, principal at Tor Bridge High, said: "All new students when they start at Tor Bridge High are given a home/school agreement that gives parents and carers details of our expectations before their children begin with us in Year 7.
"Miss Anderson has signed this home school agreement.
"It clearly states in our uniform policy that haircuts under a grade two are not allowed.
"As a school we are extremely supportive and proud of our students who are involved in various cadet groups and have a number of students who belong to these organisations whose haircuts do not breach our uniform policy."
The case is the latest controversy involving pupil's hair as several schools brought in stricter regulations for the start of the new academic year.
In another incident three weeks ago a 13-year-old girl hit the headlines after she was sent home from school in Sheffield because her head was shaved on one side and dyed brown and blonde in the pattern of a leopard's skin.