Hmm, I live in an area of London where selection at age 3 happens in some selective independent schools. (off the top of my head, I can think of Putney High, Wimbledon High and possibly there are a couple more). Interestingly, these are all girls schools. I can’t think of any boys schools or co-ed schools that have a formal selection process at 3/4. Perhaps this is because boys are perceived as less likely to focus at that age, or their fine motor skills develop less quickly? I’m not sure?
At age 3/4, they are not really looking at who can read such-and-such words, or who can write their name neatly etc etc. There is a vital difference between ‘learned ability’ and ‘underlying ability.’ Parents can drum into children the former, but not so much the latter.
Having said this, any selection at such a young age is likely to be a very blunt instrument indeed. The ones who are selected are the ones more willing to engage with the assessment process. I guess they are looking for ‘teachability’ as it makes the teachers’ lives easier if they can hit the ground running in reception and don’t have children who are unfocused or ‘not ready.’ But, as we all know, children develop at very different rates. Some of the brightest children will almost certainly be missed at age 3 - for all manner of reasons eg. many exceptionally bright children may appear a bit ‘preoccupied’ at that age or their train of thought may not be what the test assesses. Others may lack confidence or not have the best social / communication skills. The two do not go hand in hand!
Boys schools tend to assess at age 6/7 and even then, it’s a very blunt instrument. That’s not to say, the ones who are selected don’t deserve the places, but just that many more equally able children will be missed.
For instance, my son had some dyspraxia at age 6 and could barely hold a pen or co-ordinate himself. He could read pretty fluently, but how could he sit and write a timed story in 30 mins when he couldn’t hold a pen properly? He didn’t get into any of the selective schools at 7+, but by 11+, when his motor skills issues had resolved themselves, he got into them all.
So to summarise, a few girls’ schools select pre-reception, but these schools will also have selective entry at 7+ and 11+. The older a child is, the more certainty there is about their particular ability and learning styles. Some of the children selected at 3 will inevitably drop out as it turns out not to be the right environment for them after all (eg. you can’t really diagnose dyslexia or other SLDs until at least age 7). Basically, there is such a hoo haa about selective schools in London and it’s a minefield, frankly! They can get away with it because the demand for limited places is so high. No idea what it’s like in other parts of the U.K?