Mr Walker had been drafted in as headteacher of Park View in Haringey, a Fresh Start school which replaced the locally notorious Langham secondary.
He admits he was surprised by some of the horror stories about behaviour he heard from parents when he took on the job in 1999. Other problems included an erratic heating system and rodent infestations in some buildings.
Adding to Mr Walker's difficulties was the growing consensus that the Fresh Start approach did not work. There had been a series of ineffective relaunches elsewhere - including one in Brighton where he had previously worked as assistant director of education.
"I underestimated the challenge," Mr Walker said. "I remember there were press reports about three heads at Fresh Start schools leaving and someone asked me 'Are you next?' " Five years later and Park View's reputation is now so good that parents only stand a chance of getting a place if it is their first choice.
Its success is striking as it had previously been considered the worst school in Haringey. But the improvement is far from unique in a borough where all five of the worst performing schools have seen dramatic improvements.
Park View's intake is diverse: more than 60 per cent of its pupils speak English as an additional language and around the same proportion are eligible for free meals. Yet it has managed to triple the proportion of pupils getting five top grades at GCSE to 39 per cent.
At Gladesmore school GCSE results have doubled over three years, while at White Hart Lane they have quadrupled.
The several of the schools have benefited from new leadership and extra investment through the private finance initiative and other grants. Park View has benefited from pound;10 million of building work.
Ideas developed at one school, such as White Hart's decision to teach pupils in some lessons in their home language, are now being copied by others like Park View.
The Haringey schools have also benefited from more focused support from the education authority, which in 1999 had been in such disarray that the Government sent in a private company to intervene.
Sharon Shoesmith led the Capita team which worked with Haringey until this August and is now the borough's director of education. She describes the changes as "the most successful turnaround of an education services department in the country".
One of the few schools in the borough to see results fall is the pound;15m Greig city academy. It is outside local authority control and part of the academy programme which replaced Fresh Start (see below).
Mr Walker said the LEA changes had been significant but he believes the main reason why Park View has succeeded where other Fresh Starts have failed is that parents were convinced the transformation was more than just a new name and uniform.
More than three-quarters of the teachers were replaced when it was relaunched and its timetable was totally restructured.
Another boost for Park View was becoming the first school to gain joint language and performing arts specialist status.
"In the first two years I never heard a complaint from a parent about the curriculum or their child's homework," Mr Walker said. "We now have parents who ask those hard questions."