It should go reasonably far. Each of the 21,000 primary schools (of which I know more about than secondary) are within an administrative area. Generally, the people who head ICT training in these administrative areas are not developers. Furthermore, in the UK primary sector, there exist quite advanced mechanisms for transferring "best practice" from one school to the next. The UK gov't spends real money on this and gets real results in turn. If you train 100 teachers in the current pedagogical best practice for teaching software development, this will (at some level) feed into more than just their school. Ideally, you will see the head ICT trainers in an area being drawn from this initial pool of 100. Or, at the very least, advised by them.
I think this approach, even given the small numbers invovled, is better than previous approaches from the private sector. Previous approaches have involved throwing software and/or hardware over a wall and expecting teachers to know how to integrate it into the curriculum. I'm cautiously optomistic.