An Islamic school has been "unlawfully segregating" boys and girls for all activities except weekly assemblies.
Ofsted said pupils at Redstone Academy in Balsall Heath, Birmingham, were not safe and procedures were disorganised.
"Boys enjoy school more than girls. This is because they are treated favourably and have more privileges," an Ofsted report said.
The school's headteacher said the idea boys were given favourable treatment was "just not accurate".
The academy, which has 152 pupils and charges up to £2,885 in annual fees, was visited by Ofsted in November and rated as inadequate.
Of the privileges afforded to boys, such as more sport opportunities and first choice at work experience places, the report said: "Some of the girls told us that they do not like this. They said that this was not fair and feel disadvantaged."
The school, which teaches children from 11 to 16, only permits pupils who are likely to gain a strong pass to complete their GCSEs in subjects including English literature, history and Arabic, which pupils said limits their options for college, inspectors added.
Other criticisms include:
- School provides an inadequate quality of education
- Pupils do not develop writing skills well enough
- Not enough done to prepare pupils for life in modern Britain
- Confused understanding from teachers about careers
- Not enough done to ensure pupils are safe, with leaders not ensuring appropriate risk assessments are in place and ineffective safeguarding plans
- A significant fire risk in the school and pupils with serious allergies not having the care plans or medicine they need
But pupils told inspectors there was very little bullying in the school and the school's rules are clear and, mostly, pupils comply.
Headteacher Saadat Rasool said the school was waiting for "formal approval" of a move to split into a boy's school and girl's school, but had been considered by Ofsted as one entity.
"We work very diligently to offer the best to both boys and girls at our school — and both are given equal opportunities to be successful in whatever they choose," he said.
The Islamic faith Al-Hijrah school in Birmingham was also found to be unlawfully segregating its students, a Parliamentary committee heard last year.
Follow BBC West Midlands on Facebook, on Twitter, and sign up for local news updates direct to your phone.