Can someone explain the state school catchment system to me?

I think it is much easier to move from UK to US after the end of year 9 than the other way around. The History will be different though, but no bad thing really, it could help him become a real historian.

Thinking about your eldest , if he arrives into Year 9 then you may want to look at how/when to reintegrate him into US system. Here during Years 10 & 11 the curriculum is based on GCSE courses, usually each 2 years long and some including modules and assessed coursework. He may not have long after arrival in which to choose his options as he will only be able to take so many subjects forward. To an extent that many be dictated by the focus and resources of the school he is allocated (ie Arts, Science, sport etc) Would you be planning to stay until July 2015 to enable him to complete the exams ?

Ickenham is only a 10 min walk from west ruislip station and schools in the area are good. Parts of ruislip similarly are just a walk to the station. Not central London but close enough to visit and some good schools.

Scuba cat, have a look at Leighton Buzzard in Bedfordshire - the train to Euston can take as little as 30 mins, and the secondary school has a good reputation. I live not far away. and pretty much all the schools I've come across in rural and small-town Bedfordshire seem to be pretty good. And your housing budget could get you a nice house in these parts! Bedfordshire is far less sought-after than, say, Surrey or Buckinghamshire, so is cheaper, but is just as nice and has decent schools and direct trains to London.

London commuters get very adept at dog-legging their walk - avoiding main streets by cutting through districts using side streets. It's a great way to see the city. On a walk from City Thameslink to Holborn, your DH would zip diagonally through the Inns of Court - peaceful Dickensian green squares, beautiful buildings, a great walk in the morning.

In Guildford, my DH walked up to 1/2 hour to the Station, you could also use a folding bike. Walking is a big way of getting around, especially in London. It is often faster and more pleasant way of getting around than the tube or waiting for buses. You DH will definitely want an Oyster card as well. However an alternative would be to use a Boris Bikes. The climate is probably similar ish to Seattle but the South of the UK gets little snow usually, due to its maritime climate and the jet stream, London is usually a few degrees warmer than the surrounding counties due to the Heat island effect. It can get piercing cold, due to cold and wet winds sweeping along the Thames. Chancery Lane is supposed to be 9 minutes walk from Farringdon, TFL puts walking from Farringdon to Holborn as 14 minutes,but Holborn is such a vague area it could be far less.
If you are coming for a visit, I would suggest also seeing how far the distances will be for his journey.

If you are buying an annual season ticket it will be issued as a Gold Card which will also double up as a discount card in the south east. It is also normal to get a loan from your company to pay for an annual season ticket.

I checked out the walk time on the Transport Direct journey planner by the way - could be useful if you can find a postcode like a school or office as it covers the whole country and every single transport possibility!

honestly, most people walk that sort of distance! It's 13 minutes ... takes longer to change platforms on the tube.

Check that the ticket doesn't already include travel within Zone 1 as City Thameslink is in Zone 1 already.

Snow and really heavy rain is a very rare event! Drizzle is far more common, and snow is often only a very light dusting.
Boris bikes are a great and very convenient way of getting around, my DH uses them whenever he has to go into London now.

Compare weekly train season ticket from Wimbledon to Waterloo with zone 1-3 Travelcard.

Train season ticket £21.30
Oyster pay as you go (10 x peak singles) £31
Travelcard £34.20

You can choose tube or train from Wimbledon but the train is often quicker and on its own it is cheaper.

Scubacat, if he's commuting in from say, Morden or one of the nearer Thameslink stations, he'd probably be doing it on a Monthly or Annual Travelcard anyway - which covers any bus, tube or train travel within those zones, and at the weekend too. So hopping on a bus would be free. Often quicker to walk in Central London, but once you know your bus routes it can save a few minutes if the right bus turns up.

www.tfl.gov.uk/tickets/14416.aspx (news to me that there's a Zone 9, not sure how far out that goes).

If it snows your main problem is whether the train is running on time. But central London is like a microclimate - it is always two or three degrees warmer than the suburbs! So snow doesn't stick.

You need a travelcard for the tube anyway or pay as you go with a precharged Oyster card. For train journeys you can get a travelcard (and use the bus/tube on top), pay as you go with Oyster (cheapest if you are part-time) or get a point to point season ticket which can be cheaper than a travelcard.

Re walking in the winter, London weather is much better than you'd think. There are surprisingly few days when it rains too hard for a ten /fifteen minute walk to be a problem (and when it does that's what umbrellas are for) and bitter cold / snow is likewise a problem for a handful of days each year.

Subcat, I'd say muminlondon is right - at Holborn/Chancery Lane, the tube is not your only option; City Thameslink station is close by (check it on Google maps). If it were me, I would concentrate on a shortlist of affordable towns and suburbs along that mainline route - say St Albans in the north, perhaps Bromley or Beckenham in the south - because the combination of a wider, bigger station and direct train lines is likely to add up to a much more comfortable, quicker commute than by tube. St Albans is lovely and schools are great, but it's not London. Beckenham/Bromley are reasonably safe and pleasant London suburbs with good - and some great - schools. There are plenty of other options.

If you are doing a reccy trip, do a dummy run of each commute at peak week-day time if you can. Don't do a dummy run at weekends - the timetables are different, some lines don't operate and the transport system is generally much less crowded, so you won't get a realistic result.

People do use scooters (mopeds), yes, and they're not subject to congestion charge. Generally they don't use push-along scooters, though - bit antisocial on crowded pavements (not sure which you mean!)

scubacat, you could easily avoid the tube if you get the train. Within London zones I don't think there's a price difference between tube and train. You can end up at Waterloo, City Thameslink or Blackfriars stations and be within 15 minutes walk of Chancery Lane. The map is very misleading - central London is much smaller than it looks and much of it can be walked or you can hop on a bus. Have you looked at the Transport for London website? There's a journey planner so you can test journey times.

Central line is fast and more modern than the Northern, and as someone else said, not having to change is a huge time saver. Ruislip to the west, or perhaps some of the Essex towns such as Epping, Hainalt to the east, would give a trouble-free inward commute. But it will always be packed in the evening - I usually had to let one or two trains go before I could get on a train at Chancery Lane. City Thameslink station with its links to towns and suburbs in the north and south is bigger, though will still be crowded.

Wifi only in a handful of tube stations and trains: my.virginmedia.com/wifi/index.html

London schools are outperforming those in the rest of the country, according to a recent Financial Times study: www.bbc.co.uk/news/education-19151471

It depends what he is doing. Honestly some companies are really in favour of "presentism" and like to see you there. However sometimes you can get in early to get out early (can make a huge difference) or even stay later and be able to get in later.

The LA/borough have to supply you with a school place in a reasonable time, but that could be a month. They could drag their feet and it could be longer. In the meantime you either give them a holiday or homeschool them.