Understanding levels and how they are graded

[RoadArt]

I know that there is a generalisation that a child should be a level 4 when they leave school, but about 20% will be on a level 5.

But how does a teacher actually assess this? There is so much to learn within each level, and there are various strands for each topic.

Kids might be a 5a in one area, for example fractions, but only a 4c in another area, for example areas and a 5c in addition but a 4b in subtraction.
What criteria do you use to assess the child?

When would a typical average child complete the Level 5 and are there a lot of children at high school only on Level 3?

I am intrigued by this and would welcome any feedback

oh lordy, what a huge question. The gist of assessment first is that there are all sorts of pieces of evidence that we use to assess children's work, the most well known of these probably being the KS2 SATS that children take in the summer term of Y6, but there are constant assessments being done right through the school year in every class. As you may imagine, we need it in order to plan.

A child wouldn't be assessed in addition and subtraction separately, as this all comes under the heading "number" (impressive title, hehe) Just to clarify, there are also the other topics of data/data handling, shape, space and measure, and we work our way through all of these in the average school year. The national curriculum and the various bits of other government 'guidance' and strategy paperwork are quite prescriptive about what we teach, tbh. That assessment is a huge part of what teacher training is. The descriptors are fairly clear and we can usually ascertain precisely what level a child is at. Targets also state that they're supposed to move two sub-levels each year... most do, some don't.
I've not answered all of your questions, it's going to be one of those things that hopefully a good few people will wander in to share on!

Thank you. Its not really a question I want to ask at school but I am curious!

I was just generalising on the grades as an example.
(DC using Maths Whizz at the moment and they break up the topics into sub categories.)

well mn is the best place to ask, isn't it

TBH the generalisation about the level 4 is a reasonable one, but with our current yr 6 we'll only have a couple at level five, half a dozen at level 4 and the majority at the better end of level three. I also teach occasionally in high schools and there are many many year 7 and 8 children who make only level three to four in literacy and numeracy. There's teacher-speak like a "secure 4b" which implies that a child has all of the concepts as opposed to some or most of them, one with a consistent standard, if that makes sense - rather than a child who can do number, data, shape but has no clue about measurement, for example.
I'm rambling now... and I've got to be up at 7
time for beddy byes