Akhan, the correct way to challenge the council on their figures is through the Scrutiny process.
The council's numerical forecasts for secondary school places were first published at the request of the Education & Children's Services Scrutiny Committee 1 week prior to their 21st November meeting. The minutes from that meeting have not yet been published, but it was a public meeting and I was there so I can give you a personal account of what happened.
As well as the council's forecasts, the committee members had been sent a copy of RISC's response (an earlier version of this one combined with its appendices). That had been produced by Jeremy Rodell (who has a professional, numerate and analytical background), using publicly available data, in the few days between the forecasts first being published and the meeting taking place. However the committee members had not had it for very long and some had only received it that day.
The Secondary School forecast paper and appendices were considered under item 8 of the agenda. Jeremy Rodell was there and gave a short presentation to the committee, drawing its attention to his analysis and the potential risks he had identified in the council's forecasts. The committee then questioned the Director of Education, Cabinet Member for Schools, and the Head of School Commissioning. The questioning was intense by some of the committee members. One committee member asked if the council would be responding to the analysis presented by Mr Rodell, and the answer from the Director of Education was yes. Their tone was respectful and while they had not yet had time to fully consider the RISC paper they seemed willing to listen and respond appropriately.
One committee member proposed that, as the forecasts were to be presented at Cabinet three days later, the committee should send a message to Cabinet to convey that there were risks associated with the forecasts. There was some discussion about the wording, and some members didn't think it was necessary to send such a message. Ultimately there was a vote on whether the committee should send a message or not, and it was decided that no message should be sent.
At the subsequent Cabinet meeting, Jeremy Rodell again gave a presentation. However, the Secondary School strategy, based on the council's forecasts, was approved.