For the past year, Mr McCarthy has been seconded from his job as head of Eaglesfield school, a 1,000-pupil boys' comprehensive in Greenwich, south London, to work with British Telecom investigating the best practice for installing information and communications technology in schools.
The last time Whitehall poured money into schools to help them embrace the age of new technology, it was the mid-Eighties, Kenneth Baker was in charge and the aim was to get a computer into every school. Some of them, it is claimed, are still in their boxes.
Mr McCarthy has been asked to ensure that this time - with the commitment that by 2002 every school is on the Internet and every teacher is trained to use the equipment - things will be different.
It has been a comprehensive review. In eight weeks, Mr McCarthy and a team of four other teachers around the country - all paid for by BT - visited more than 300 schools where they knew good computer systems had been installed: they wanted to discover exactly what mistakes those schools had made, what they had done right and what advice they might have for those following in their footsteps.
By next April, each school that wants to benefit from the #163;220 million earmarked for training staff in computer matters will have to produce an ICT policy if it is to get any money at all. This money is yours by right, but it is conditional on you working out how your school is going to integrate technology into its teaching.
There's #163;500 per teacher available for training but Mr McCarthy believes that schools need to think carefully about how they spend that money.
Primary schools, he suggests, would be better advised paying for two teachers to be fully trained (up to #163;2,000 each) rather than dividing the money among the whole staff. The trained staff could then show everyone else what they have learned.
"There is going to be some cultural resistance to the innovation of technology," says Mr McCarthy, "but we need to use the enthusiasm of the minority to carry the rest."
But where do you find good training? Mr McCarthy thinks you should ask your local authority adviser to steer you towards the better firms. You might also ask advice from the National Association of Head Teachers or the Secondary Heads Association.
It is in primary schools that he is most anxious to get the message across: because of their size they often lack the resources (personnel and money) to cope. But from this term, they must tackle the ICT requirement of key stages 1 and 2 of the curriculum (as if they won't be busy enough taking on the literacy and numeracy strategies).
He believes that primaries, like all schools, need to see ICT as a tool to support learning. The technology should underpin the rest of the curriculum and not be an end in itself. So he draws a distinction between generic training and subject-specific training.
He is not sure that tax breaks to allow teachers to buy hardware can be justified. But they need to get their hands on machines to learn the basics somehow. Borrowing machines from the established companies is one idea worth exploring, he says.
POINTS TO REMEMBER
The average primary school can equip itself for #163;20,000.
* Primary schools should think seriously about creating a suite of rooms with 13 or 14 machines so that classes can work on projects together.
* Training money could be better spent by concentrating it on two teachers to make them specialists so they can then train the rest of the staff.
Pat McCarthy's report will be published by BT in November