Ofsted judged Walworth Academy to be "a good school with outstanding capacity to improve" in its first full inspection of the academy since it opened in 2007.
The inspectors said: "Walworth Academy is in the business of transformation. It has transformed itself and is now a good and rapidly improving school whose students make good progress academically and great leaps in their personal development. Most importantly it is transforming the lives of the students who attend the academy."
The inspectors singled out "the significant successes that have been achieved in rapidly increasing the rate of progress made by students; significantly improving attendance; widening horizons; ... raising aspirations; and preparing students for the next phase of their education. ... The quality of care, guidance and support offered to students is outstanding."
In her letter to pupils, inspector Emma Ing wrote: "We agree with you that the improvements that the academy has made in the last two years are breathtaking. We share your view that the teachers are extremely well led by the principal and that they work tirelessly on your behalf. We can see why you feel safe and extremely well cared for and proud of the academy."
Walworth Academy principal Devon Hanson said: "We're pleased that Ofsted recognised the commitment and effort Walworth Academy makes to ensure that its pupils achieve the utmost they can during their time with us.
"Helping our pupils to 'Be the best that you can be' really does govern everything we do as a school. It informs our determination to raise attainment, to improve attendance and behaviour and to continue to raise our standards of teaching and learning support.
"I am immensely grateful to the families of our pupils for their support, to our governors for their commitment to the school and to our pupils and staff who have utterly transformed the academy and its ambitions in a very short time. I am determined, for the sake of all our pupils, that we will make Walworth Academy an outstanding school and I'd like to thank everyone in the academy for supporting that aim."
However, the quality of teaching at the school was given grade 3 (satisfactory). As Emma Ing's letter to pupils said: "There is some excellent and some good teaching at the academy, but we noted that there is too much teaching that is a little bit slow, a little bit dull and not sufficiently challenging of you all."
The inspectors also found the school had been "over-generous" in its self-assessment and called on staff to do more to increase attendance levels at the academy.
During the general election campaign David Cameron described Devon Hanson as "a great man".
He said: "He's one of the most impressive headteachers I've met. When new kids are going to his school he goes to the parents' home and sets out with them a little contract about how the parents are going to back the school and how kids are going to behave.
"I think he's running a really great school. I think more academy schools in neighbourhoods like this make a real difference."