Liam Scholes, 11, arrived at Sale High School in Trafford, Greater Manchester dressed as the erotic romance novel's male protagonist Christian Grey - wearing a suit and carrying cable ties and an eye mask.
The boy's mother, Nicola Scholes, 36, said she was called by teachers who said his costume was not suitable and he would not be able to participate in events for the annual celebration of reading.
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Liam Scholes arrived at school on World Book Day dressed as Christian Grey and equipped with cable ties and an eye mask
The school marked World Book Day by asking pupils to dress as famous literary characters.
But Ms Scholes is unrepentant about her choice of outfit for her son, telling ITV1's Good Morning Britain: "I don't regret allowing him to go as that character.
"He's a character that has been put out there on the television and all aspects of media.
"Every child at the age of 11 knows who he was. He walked into school yesterday and every child knew who he was.
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His mother Nichola says she has no regrets about her choice of outfit
"I don't think he's gone as something that has not been accessible to children of his age before."
Liam said: "He's the character that has been talked about the most in the past few years and he's just been everywhere you go."
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Jamie Dornan plays Christian Grey, a bondage-obsessed billionaire
He added: "I think it's the content of the book that might (make) people think that it's inappropriate. But I went into school as Christian Grey just for a laugh, not anything else."
A film based on the book by EL James - which has sold over 100 million copies worldwide - hit screens last month.
Campaigners claim the story of billionaire Christian Grey's passionate relationship with student Anastasia Steele promotes domestic abuse.
'Fifty Shades Of Grey': Where Do You Know The Cast From?
Jamie Dornan (Christian Grey)(01 of10)
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Let's start with the obvious, shall we?Leading man Jamie Dornan is probably best known for his role in 'The Fall', but you might recognise him from the film 'Marie Antoinette' or the TV series 'Once Upon A Time', where he played The Huntsman.That said, you just might have seen his impressive Calvin Klein underwear ad campaign a few years ago too... (credit:Jon Kopaloff via Getty Images)
Dakota Johnson (Anastasia Steele)(02 of10)
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Daughter of Don Johnson and Melanie Griffith, Dakota starred in 'The Social Network' and '21 Jump Street' prior to landing the part of the leading lady in 'Fifty Shades'.She also starred in the final episode of the US 'Office', and - like her co-star Jamie Dornan - has also done some modelling work. (credit:Gardiner Anderson/Bauer-Griffin via Getty Images)
Eloise Mumford (Kate Kavanagh)(03 of10)
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Fresh from her roles in TV shows 'Lone Star' and 'The River', Eloise has landed her biggest role to date as Anastasia's roommate and confidante, Kate. (credit:Jim Spellman via Getty Images)
Jennifer Ehle (Carla Wilkes)(04 of10)
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Over the course of her career, Jennifer has bagged two Tony Awards for her roles in 'The Real Thing' and 'The Coast Of Utopia'. She was also awarded the Best Actress TV Bafta in 1996, for her portrayal of Elizabeth Bennet in 'Pride and Prejudice'.More recently, Jennifer starred opposite Colin Firth in 'The King's Speech', and also nabbed roles in 'Contagion' and 'Zero Dark Thirty'. She's playing Ana's loving but often-absent mum in 'Fifty Shades'. (credit:ROBYN BECK via Getty Images)
Victor Rasuk (José Rodriguez)(05 of10)
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One of Victor's biggest pre-'Fifty Shades' roles was in skating film 'Lords of Dogtown'. A method actor, Victor tried to remain in character at all times, leading to him fracturing one of his orbital bones while skating in his spare time. Ouchie.He also appeared in 'Godzilla' last year, as well as the Steve Jobs biopic, 'Jobs', where he played Bill Fernandez. (credit:Craig Barritt via Getty Images)
Luke Grimes (Elliott Grey)(06 of10)
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You might recognise handsome American actor Luke Grimes from his part in 'American Sniper', or his recurring role in the American drama 'Brothers And Sisters', where he played Ryan Lafferty.He'll be playing Christian Grey's adopted brother Elliott in the new movie. (credit:Rindoff/Dufour via Getty Images)
Rita Ora (Mia Grey)(07 of10)
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Never heard of her. Next. (credit:Steve Granitz via Getty Images)
Marcia Gay Harden (Grace Trevelyan Grey)(08 of10)
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Despite having a relatively small role, Oscar-winning actress Marcia probably has the most impressive CV of all of the 'Fifty Shades' stars.Some of the films she's starred in include 'Meet Joe Black', 'The First Wives Club', 'Whip it' and 'Pollock', which bagged her the Academy Award for Best Supporting Actress. (credit:Michael Tran via Getty Images)
Dylan Neal (Bob Adams)(09 of10)
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Dylan Neal will be playing Anastasia's stepdad and main father figure and source of guidance, Bob.After leaving American soap opera 'The Bold and the Beautiful' after two years, he went on to star in 'Sabrina The Teenage Witch' (as Sabrina's last ever love interest), 'Dawson's Creek' and, more recently, 'Bones'. (credit:Angela Weiss via Getty Images)
Max Martini (Jason Taylor)(10 of10)
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Not to be confused with the similarly-named Grammy-winning pop producer, Max Martini will be playing Christian Grey's faithful head of security, Taylor, in 'Fifty Shades'.His credits include three years in 'The Unit', and an important role in 'Pacific Rim', where he played Hercules Hansen. (credit:Araya Diaz via Getty Images)