we've put an offer in on our first home which happens to be in the catchment area for one of the best schools in our area (ie, last 2 ofsted reports were solid 1's). As DS is only 13months, I'd not really thought of been hugely bothered by it, assuming we'd only be able to afford a flat we'd have to move out of within 2 years anyway, but this one I could see us living in until he's well into school, so obviously the catchment is a bit of a bonus.
However - their most recent oftsed report is out this week and they've gone down to a 3!! surely this is weird? I've not even started looking round schools etc but now thinking maybe I ought to seeing as good schools are so oversubscribed in London, but how come the reports can fluctuate so much and should I be unduly worried?