The education watchdog has praised St Peter's Independent School for making swift and decisive action to resolve the weaknesses identified during the last inspection.
During the one-day inspection in January Her Majesty's Inspector Martin Finch said the school, which has 105 pupils under principal Julie Fenlon's leadersip, now has comprehensive schemes of work to teach a broad and balanced curriculum.
He specifically made reference to the improvement in art, reading and maths among secondary school pupils at the site in Lingswood Park, Blackthorn.
Mr Finch said: "Pupils make strong progress in mathematics in the senior school. Pupils are able to use their knowledge to solve challenging questions. Outcomes in mathematics at GCSE at grade 4 or higher are above the national average.
"Pupils in the preparatory school study a wide range of mathematical topics to gain a broad understanding of concepts. However, they do not have enough opportunities to reason mathematically."
Trips to Warwick Castle have also been up for grabs and the children have written their own brochures for the castle to inform readers of its historical significance.
Positive remarks were made about how the school teaches pupils about democracy through electing representatives to the school council and visits to the Houses of Parliament, where they met Northampton North MP Michael Ellis.
At the previous inspection, in 2011, leaders had not ensured that governors had reviewed the school’s safeguarding policy or the effectiveness of the school’s safeguarding procedures. Also, they had not ensured that all staff with responsibility for teaching children in the early years had the appropriate qualifications.
Mr Finch added: "All staff have received appropriate training about safeguarding.
"They are aware of how to report concerns and leaders take prompt and effective action when concerns have been raised.
"The school’s record-keeping of actions taken in response to concerns raised has improved over the last few months and is now robust."
The school has now made sure pupils and staff have their own toilets, their own changing facilities with a shower for the over 11's who do PE, and that safeguarding and welfare requirements for the early years foundation stage have been met.