Students at the school which sent a girl home for wearing a Union Jack dress were told to "proudly represent their heritage", it has emerged.
Bilton School, in Rugby, Warwickshire, urged pupils to "wear traditional cultural dress", according to a newly-exposed letter to parents.
However, Courtney Wright, 12, was ordered to go home for wearing a Spice Girls-style dress - which featured Britain's flag front and centre.
Wright had planned to give a speech about British history and traditions, and revealed she was "proud" to show off her "iconic" garb, but left feeling "embarrassed and upset".
WATCH: Schoolgirl, 12, reacts after being punished for wearing Union Jack dress to ‘Culture Day’
Her father, Stuart Field, had to collect her from school before the end of the day - and later said she was told culture day was "not for her".
Now, the school's beaming letter to parents has come to light.
"This special day is dedicated to recognising and celebrating the rich cultural diversity within our school community," it reads.
"This is a fantastic opportunity for students to proudly represent their heritage and learn about the cultures of their peers and staff," the letter says.
"This day is purely about cultural celebration and connection," it adds.
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BILTON SCHOOL
|PICTURED: Bilton School's letter to parents ahead of the Union Flag dress outrage
The note continues: "We encourage students to consider wearing attire that reflects their nationality or family heritage.
"Please ensure that any outfit worn is appropriate for a school setting and holds cultural significance," it says.
The controversy, according to dad Stuart, is worldwide.
He told GB News: "I've received messages from people over the last three days sharing their experiences.
"It's been a significant number with similar experiences, whether it be taking a flag down or culture days at school.
"They say it's not for British kids. It seems to have shook the hornet's nest. People have messaged from all around the world. Japan, Australia, Canada."
Earlier this week, Wright's telling-off at the hands of Bilton staff had sparked a national outrage.
Downing Street came out with a statement on Tuesday vowing that "being British is something to be celebrated".
Bilton School has since said: "We deeply regret the distress this has caused and offer our sincere and unreserved apologies."
The Rugby school has also offered the 12-year-old the opportunity to run a charity event wearing the dress - and will let her give her speech.