From his stall in the main conference room, Mr Halsall, of Justin Craig Education, told teachers the answer to their state school worries was simple: go private.
Easter revision courses with his firm at pound;300 per pupil would guarantee exam success, or your money back, he said.
"There's nothing to lose," said Margaret Wilson, head of the King John school in Benfleet, Essex. "It's a small amount of money to improve pupils'
Miss Wilson was one of 90 senior teachers at the conference, organised by the Specialist Schools and Academies Trust for schools with poor GCSE results. Previous participants in the Raising Achievement Transforming Learning scheme have made impressive gains, consistently beating national average improvements in GCSE results.
The trust does not endorse state schools turning to private crammers but is encouraging schools to look for solutions. Schools are being told to divert resources to pupils on the GCSE grade CD borderline to increase the numbers gaining five A*-C grades, the crucial factor in league table position.
Simon Morris, head of Esher high school, said he recently paid up to Pounds 2,000 for 27 of his borderline pupils and four teachers to go on a two-day residential course.
He offers Saturday classes for pupils struggling to get C grades, with extra pay for staff. Results have rocketed from 37 per cent of pupils getting five good GCSEs in 2005 to 58 per cent last year.
Mr Morris denied it is unfair to focus on borderline cases. "If people realise you are doing your best for pupils, those kinds of questions don't come up," he said.
Ani Magill, head of St John the Baptist school, Woking, explained the importance of pupils doing at least eight GCSEs - any fewer would have a negative impact on schools' value-added rating.
Schools were encouraged to be stricter about GCSE options: pupils should only take subjects in which they can achieve good results or they risk bringing down their school's value-added scores, Miss Magill said.
Mary Neal, assistant head at Highdown school, Reading, questioned the approach: "What are we focusing on - what's right for the children or the points they score?"
But David Crossley, director of achievement at the SSAT, said advice on borderline pupils was only part of what was offered to schools. He also defended the focus on CD pupils.
"These children are often the forgotten group," he said. "Schools want to maximise pupils getting C grades because of the life chances it gives them.
If a pupil is near to achieving that and we can open the door for them, we should."
Durham county council is targeting borderline pupils, providing three days of Easter lessons for 250 of them. Knowsley has run Saturday master-classes, mentoring and pre-exam workshops.
And Justin Craig Education is not the only private revision firm chasing schools' business. For those seeking to cram in style, the Institut Midi-Langues in Perpignan, on the Cote Catalan in south-west France, is offering GCSE and A-level French courses at around pound;375 per pupil for a week, including accommodation in a chateau.