Kelly Smith was shocked when she found out teachers had ruled her 14-year-old son Jason Kirkbride's short back and sides was "inappropriate".
He was given detention and put into isolation with no breaks for three days when teachers deemed his number one grade cut was against school rules.
The appearance policy Hodgson Academy in Poulton-Le-Fylde, Lancs., states that boys should not have hair shaven shorter than a number two grade and pupils breaching those rules face detention or isolation until the hair grows out.
But Kelly believes the style makes her boy look smart - and argued his education is more important than his hairstyle.
She said: "I feel his hair looks smart, fresh, neat and tidy. Not only that but having shorter hair is more hygienic.
"I don't understand how a haircut could be distracting, or make my son not look smart unless it had some fancy designs or colour.
"It's nothing to do with his education.
"I find the school policy ridiculous, and a number two can be too long. This would mean regular trips to the barbers, and sometimes this is not possible.
"So a shorter cut would be better as it lasts longer."
The school's policy says the final judgement as to what constitutes an inappropriate hairstyle is taken by the senior assistant headteacher or, in her absence, the headteacher or deputy.
Jason had his trendy chop done after school on Friday, September 27.
Mother-of-two Kelly decided to get a number one grade, a bit shorter than he usually gets, so he could go longer in between trips to the barbers.
But when he returned to school on Monday, September 30, he was placed in isolation for three days as teachers ruled it breached the school's policy.
Kelly, of Hambleton, Lancs., said soldiers in the military have their shaved and it looks "smart and sharp".
She added: "If it is good enough for the Queen and the government, why is it not good enough for a school?
"He was allowed back into class on Thursday, his hair hadn't grown that much in those few days. I think they were just making an example of him.
"He was really upset about it. He came home and couldn't understand why he had been given detention for his hair.
"One of the teachers even joked they were going to get a ruler out to measure how long it was as it grows.
"I get this is not the end of the world but when did we start worrying more about which grade of hair cut a child received other than their education this should be top priority.
"Sometimes students have long unkept hair and can look untidy, again nothing to do with education more about personal preference.
"People say the school is getting children ready for the world of work, but I've never known a job not be given to somebody because of their haircut."
Hodgson Academy refused to comment.