A 15-year-old was banned from school for a week because her skirt that she has been wearing since September is now "too short".
Her mum Zoe Graham has spoken of her frustration as her daughter is now unable to attend her mock exams due to the school's decision.
The 37-year-old carer told Nottinghamshire Live her daughter has been wearing the same skirt all year long and "never had a problem before".
The teenager was sent to isolation on Monday after being told that her skirt no longer meets the uniform standards.
The school said it is a new policy and it is "continuing to communicate with families to provide additional support, including offering free clothing and shoes to individual pupils as needed".
The teenager continued to attend classes at Nottingham Academy on Greenwood Road until Wednesday morning when Mrs Graham received a phone call from the school.
The mum was left fuming when she has been told that her daughter has been banned from school until next Monday.
Mrs Graham said: "They cannot do this because my daughter needs to be in school.
"She is already dyslexic.
"And they sent her to isolation and she refused.
"A child should not be isolated over a skirt. She has done nothing wrong."
The worried mum said that she received a letter from the school earlier in June, informing parents of the uniform policy change.
According to the Nottingham Academy's website, the skirts must be "no shorter than knee length".
"She has been wearing the same uniform since September. You cannot expect pupils to get new uniforms overnight."
Mrs Graham added: "She is supposed to be doing mock exams this week and she is not allowed in school. I am at a breaking point and I do not know what to do as a parent."
A Nottingham Academy spokeswoman said: “We set the highest expectations in every part of school life to ensure all pupils can achieve their potential.
"As part of this, we recently updated our behaviour policy, which includes uniform expectations.
"We appreciate this is a new policy and are continuing to communicate with our families to provide additional support, including offering free clothing and shoes to individual pupils as needed.
“We are also committed to ensuring all pupils are supported with their individual learning needs and have robust procedures in place, including working with experts, charities and relevant organisations, to ensure they receive the full educational experience and that their health and wellbeing is supported and enables them to thrive.
“While it would be inappropriate to comment on individual circumstances, we would like to reassure our entire school community that we will continue to maintain our high standards to ensure every child has access to the best possible education and is empowered to fulfil potential.”
