I disagree. Mainly because its certainly possible lots of peoples kids are not reaching potential at uk state schools.
Somewhat the percentiles say 20-80 are quite fluid and parental input, teacher effort etc can make the difference.
I would say dd1 (12) is capable of say top 5%. She came 9th percentile maths in sats and only about 25th percentile for reading. But she could do all the maths just cant stop making silly mistakes.
At secondary after y7 she is coming out only about top third of the year group. So thats not great. Its partly her (sen) and not working fast enough so not finishing tests.
As a parent its hard to see schools not put the effort to move kids from meeting expectations to exceeding. In primary no effort was made till sats.
But last week y8 dc got 37/60 on a maths test. So its hard to look at the paper and see she could easily have got 57/60. But 6w of no school straight into a test with no revision. So even for 1 dc the gap between achieved and potential was 33% of the marks. And that result would i expect have put her in the top 10% of the year.
My other dc also hasnt been stretched at primary (she can do work 2years ahead in maths). Got 111 on ks1 sats but again no extension of homework etc.
Average in itself is a wide range. Do you mean met expectations?
As also in y5 and y6 teachers wouldnt accept dc could get exceeding maths bht she did at the end of y6.
A lot of exceeding kids do extra at home so may not naturally be brighter.
If you mean at gcse i guess yes most parents want their kids to be getting 6+ whereas average would be perhaps a 4/5.
It doesnt help that noone talks about dc abilities or achievements so you actually dont know how your kid did relative on SATs or other tests.
Some kids really got helped by primary to get high sats maths etc (reaching full potential) but 2 of these i know then have struggled in higher maths sets.
My sister was really clever so my 10 gcses (2A/7B/1C) dixnt look good at all.
Some kids slow to learn to read exceeded in all SATs (marathon vs sprint)