If you live in a non grammar school area...

No grammar here in SW16 but there is a heavily over subscribed comp (2000 aplicant for 200 places) and it is selective.

Our local secondary has a good reputation as does the nearest one to it. We are not in the catchment area (not called that anymore but ykwim) by chance. When we moved to this location, we checked out the schools and bought a house in this town because of the school's reputation (and other reasons).

There is a regular influx of families moving to the area from the nearby city (their children joining the primaries from about Year 3/4 onwards) so that they can go to the secondary school here rather than one of the secondaries in the city which have a poor reputation.

So yes, my children are attending the nearest school, but only because we deliberately moved near to it. Other people do compete for places at both the good secondaries from outside the catchment areas.

We border two other counties. We are in County C, the other counties are A and B. County A has excellent state schools in the nearby town and, except for very particular reasons, no one from County C goes to schools in County A. County B has a different school system (first/middle/upper) and the local town is less socially desirable (how can you put this in a nice way) but has very nice villages around it.
In my area in County C, we have only one state secondary school and as it is a rural area the only other choice is to get on the bus to the county town 10 miles away where you could go for a place at the church secondary (if you have your forms signed by vicar etc). Our local state secondary has much better results than the schools in County B, so lots of children from County B apply to go there - and in order to do this they have to attend the County C primary schools for at least two years.

lots of competition apparently and a very very clear effect on house prices.
But our dd is not 2 yet so we haven't looked into it in detail, just clocked that if we want her to go to a good school it's hard cheese unless we suddenly become a whole lot richer