If I was choosing an infant school I would pick one where reading is taught properly by synthetic phonics. (Ie. no mixed methods)
The intake of my son's infant school has been described by Ofsted as well below average. The school is in deprived area and there are a lot of children in the class with special needs. (Including my son who only has 40% hearing at the moment due to glue ear)
However more than a third of the children got a level 3 for their keystage 1 SATs last year. Also about half of the reception class can now blend and segment words in their reading. They have been taught to read by pure synthetic phonics. Most the children who havent learnt to blend have reasons that they are finding reading difficult. For example several of the children have very limited English.
Andrew is doing amazingly well at reading inspite of having a hearing impairment. He is moviated by wanting to read "Power Ranger" comics. His comprehension is behind his decoding ablities but that is coming on nicely too. His maths skills are developing quickly as well.
I find the concept of IQ extremely questionable. A lot of special needs that four years old have are temporary. (My son had physio, because the tendons in his heels were too tight and made it hard to walk. He also has glue ear which he will grow out of.) Even if you look at children without special needs, Xenia's children who got rejected by their first choice of school have gone on to do well.
Even with Adults there are so many types of intelligence. Things like social skills are not easily tested by an IQ test.
I am not against selection, but I think thirteen is a better age for selective education. If there was a choice of schools for thirteen year olds then I am sure that behaviour would be better. I even suspect that many thirteen year olds would select the best school for them if there was a choice of vocational, grammar schools and basic skills schools like Germany.