Hi.
I may be completely wrong here, but I have heard, maybe from 'unreliable sources', that Compton somehow 'selects'. It's a small school, I think yet gets oddly stellar results. I'd imagine there's certainly house-price selection going on there, for sure!
My DCs completed primary at Knightwood, one going into Y6, the other into Y4. We moved locally for the secondary which really is 'stellar' (Thornden).
I'd call KW a good, solid, workmanlike school; maybe not a thrilling learning environment but very good results, very good teachers, by and large (you'll always get the odd duff fit between a DC and a teacher in a school career, won't you?) and with very 'school-ready' DC, largely white but with a good proportion of other ethnicities, plus very few social problems. You could certainly rent in the catchment- we did originally, and a 3 storey 3 b/r town house cost us £850 pcm. You'd get cheaper though all of this neck of the woods is quite expensive.
Scantabout's area is a bit cheaper, and, I must say, from what I'd heard, it's a perfectly good school but I'd choose KW or Hiltingbury (or St Francis though in a different secondary's catchment) over Scantabout myself.
You seem to be looking at a large area- do you plan on moving into the desired catchment? Are you local to Hants?