Isleworth & Syon School 's strict appearance policy has earned the scorn of parents in the past, even leading to a petition signed by more than 400 parents.
With pupils returning from the summer holidays, the issue has again reared its ugly (or acceptably coiffured, depending on your viewpoint) head.
The boy's mother, who asked not to be named, said her son, who is in year 11, was sent home for having a short back and sides, with longer locks in a comb-over on top - similar to that sported by One Direction star Liam Payne .
She said the sides were cut to grade two length, which conforms with the school's policy, and it was "crazy" for him to be missing school at the start of his GCSE year over a haircut.
'He's a good pupil and he wants to go to school'
She claimed he was not the only pupils to be punished for his haircut, with others sent home or taught in isolation.
"If he had a bright green Mohican I could understand him being sent home, but not over this," she told getwestlondon .
"The school encourages pupils to express themselves as individuals, but with the next breath they're penalising them for choosing a haircut they like.
"When we were waiting outside the headteacher's office, lots of pupils walked past with almost identical hairstyles. I feel the school's not being consistent. It keeps moving the goalposts.
"This is crazy because he's a good pupil and he wants to go to school."
Earlier this year, 441 parents signed a petition calling on the school to amend its strict haircut policy.
The petition was launched after a father criticised the school over his child's exclusion for a similar haircut to that at the centre of the latest row.
He said the school should focus more on educating children and worry less about how they look.
'No apology for setting the highest standards'
The school's website sets out strict guidelines on pupils' appearance, including rules for haircuts, uniform and jewellery. It states that pupils breaching those requirements will be sent home to "rectify" the infraction.
It states that hair should be "conventional" in style and length, and no shorter than grade two. It also specifically prohibits hairstyles related to any current musical, sporting or fashion trend.
Headteacher Euan Ferguson said: "We make no apology for setting the highest standards on a wide range of school procedures and policies and we value the fact that our ambitions are shared by the vast majority of our parents and carers.
"Our Appearance Code is clear and concise and frequent reminders are given to students and their families about the expectations."
The school is not the first in Hounslow to attract criticism over its regulations about appearance.
Pupils have previously been turned away from Feltham Community College for wearing what the school deemed "excessively tight" trousers.
And in 2008, some 200 pupils at Cranford Community College staged a protest over a "heavy handed" crackdown on rogue uniform.
What do you think of the school's policy? Has your child been affected? Email firstname.lastname@example.org or tweet @HounslowBob.