The government thinks pupils at Canterbury High are underperforming, but GCSE league tables show it is one of the most impressive in the country at improving pupils' grades.
The school illustrates the paradox of the National Challenge scheme. It is ranked sixth best in the UK according to contextual value-added scores, but ministers insist it should still receive the support and supervision that goes with being a National Challenge school.
Philip Karnavas, its head, believes value-added scores are the best measure of his staff's work. While the GCSE pass rate including English and maths has remained static, if the English and maths proviso is ignored, then 90 per cent of Canterbury High's pupils achieve five A* to C grades.
"This is a stunning achievement considering we are a non-selective comprehensive in Kent's selective system," said Mr Karnavas.
The school's target this year is for all Year 11s to get five A* to C grades. Personalised learning has helped boost results and all pupils choose from a range of courses.
"We work from the premise that all students can succeed if they are motivated and engaged," said Mr Karnavas.
Meanwhile at the school with the highest national value-added score - Park Community School in Havant, Hampshire - grades have been boosted by offering pupils a wider range of courses.
Bob Carter, its deputy head, believes this approach has helped keep the school out of the National Challenge programme.
Even though more than half of the school's pupils are classed as having special needs, 85 per cent got five A* to C grades, 32 per cent including English and maths.
"The fact that our students make such phenomenal progress has helped us avoid National Challenge," Mr Carter said.
"It's a whole-school ethos - that there are no barriers to achievement and we work not only with pupils but their families."
Other schools in the top 10 include Greenwood Dale School in Nottingham, Stanley School of Technology in County Durham and the City of Lincoln Community College.
Phoenix High School in west London is also in the top 10 again. Sir William Atkinson, its head, joked he was "devastated" to have come only fourth.
Barry Day, head of Greenwood Dale, said the key to his school's success was concentrating on key subjects and GCSEs. The school is about to sponsor its own academy and will become one of the largest schools in the country, with more than 3,600 pupils, from September.