I am less familiar with the situation for tinies but can comment in Sr Cat's. I went there (rather longer ago than I care to admit!) and visit it on and off. The upper school (ages 11/12 to 18) has been going from strength to strength over the last ten years and is flying very high in the national rankings. I think it was in the top 20 on the Financial Times league table. Lots of investment in some great new facilities and quite fashionable. Day girls more dominant now than they used to be. The adjacent junior school also seems in good form and positions you well to get into the senior but there is not guaranteed translation
We are Brits returning this summer. My kids are older, 11 & 9, but have also been at Catholic school here in the US. My impression is that the Catholic system is more traditional and hence a little more like the English system. Catholic school fees here are no way near as high as UK school fees so it's worth looking into whether your company will cover them as part of the relocation.
As Joan says the good schools guide is a very valuable source of info - worth the online subscription and it will point you in the right direction for OFSTED and ISI reports on schools.
With kids your daughters' ages I wouldn't think there would be too much catch up to do. You can also get the national curriculum levels from the ofsted website, show it to their teachers and ask if there are any glaring holes and then work with the girls on covering those areas.
I would suggest you email the schools you are interested in. I knew an American family that had children at GHS (and RGS), and they seemed to do fine. I would also suggest you look at the fees, as depending on what kind of US Catholic school they are at you might find the fees a bit eye watering. Do also look carefully at salary levels (I know form my DH's company those in the US get paid 1/3 more) and the cost of living here.
however if you are moving to Guildford area, I would also suggest you look at Rydes Hill, which has a very good reputation but doesn't really select on in take. There are also a good selection of other girls independent schools within reasonable travelling distance of Guildford, all of which I have friends who have been very happy with.
We'll be returning to the U.K soonish/by 2014. Looking for advice for 6 year old and 7 year old daughters - currently at Catholic independent school in the U.S. Looking at good independent girls schools in Surrey area. Feedback/Suggestions all welcome;
1. I hear Guildford High, St Cats and Tormead are good - are they tough to get into? 2. If we arrive midway through academic year is there a chance of not getting in? 3. Just purchased a whole load of "Bond" papers for both to get them in synch with the UK students. Was wondering how effective this strategy will be?