Shannon-Leigh Harrison said her sibling was ‘turned away’ by Aspire Academy staff after arriving suited and booted in an open-top car with his date.
Today, the school said the boy was fully aware he could not attend the event due to his ‘poor conduct’ leading up to the event.
Ms Harrison claimed her brother – who she admitted is ‘no angel’ – and his girlfriend were greeted by teachers, had their pictures taken, and walked up the stairs to the Village Hotel in East Park Drive.
But then, in a post shared more than 2,000 times, she said: “The headmistress turned around to (him) and said, ‘Give her a kiss and say goodbye’.
“The headmistress of Aspire Academy accepted payment for (his) prom, let him and Lauren arrive and greeted them at the stairs and then turned him away without consulting either of my parents beforehand.
“This school is an absolute disgrace and this needs to be shared. The lack of communication and care is diabolical.”
Many people commented on the post - some urging Ms Harrison to seek legal advice - before the entire post was mysteriously removed on Thursday.
The school’s headteacher has now responded – and said the Year 11 leaver knew he would not be allowed into the event, which was held on Wednesday evening.
Lisa Shuttleworth-Brown said the prom was arranged on an invite basis, and said the school had ‘the right to withdraw the prom invitation if we feel a student has not met our minimum standards’.
“On this occasion several students failed to meet the standards required and their invitation was duly revoked,” she said.
“These decisions were not taken lightly and each individual was told, unequivocally, of the consequences of their poor conduct.
“We also left voice messages on several mobile phones to ensure there was no confusion with the families regarding these decisions.”
She said staff could not intervene until the youngster tried to enter the hotel, and added: “This is disappointing but we make no apology for upholding the values of Aspire and maintaining our high standards.”
It added that staff had been the victims of an “aggressive verbal attack” by people linked to the boy following the refusal to allow him to enter.
Earlier this year, Aspire, in Blackpool Old Road, sent invitation letters home to parents, which described the evening as ‘a fantastic celebration of all the hard work Year 11 have put in during their time at secondary school, as well as the last time they will be together as a year group’.
But it warned: “As you would expect, this is a celebratory event and it is our expectation that Year 11 students uphold our values throughout the remaining weeks in school.
“This includes high attendance, engagement in lessons, as well as meeting our behaviour expectations.
“Should a student not meet these basic requirements the academy retains the right to withdraw the invitation on a case by case basis.”
Ms Shuttleworth-Brown said any pupil banned from the prom ‘is offered a full refund’ of their £25 ticket.
Ms Harrison could not be reached for a comment.