Cloud2
Presuming you're not spoofing us here - and are not a teacher posing as a concerned? parent....
First question is what is the outcome you want from primary in general.
For me - it's that my child has a reading age = to their chronological age and can add, subtract, multiply & divide (with the proviso that this obviously may not apply to those due to disability/ illness unable to fully access curriculum). I personally think some reasonable writing skills wouldn't go amiss - able to write a paragraph answering a comprehension question on a passage perhaps? (from what I can work out that would be a high NC L4/ low NC L5 ability)
So - that leads to a second question:
Should schools be required to teach to that - well I suppose in essence that is what the national curriculum is for and things like KS2 SATs are about.
At present schools only have to get over that NC L4 barrier. The vast majority of pupils in England achieve this. www.theguardian.com/news/datablog/2013/sep/19/sats-results-key-stage-two - scroll down to tables at bottom (~85% achieve this NC L4+ threshold).
Now you're asking about the KS3 ability - officially NC Level 5 is KS3 ability (end target NC Levels KS 3 are NC L5/ L6) - roughly 50% of pupils are achieving into NC L5 ability in English and 45% in maths at end KS2 (again see guardian link above for that data). So the question isn't - surely we can't be teaching to that level in Primary - because 50% of the population are working there.
Now that can be for all sorts of reasons - here in Birmingham with state funded grammar schools of very high quality - many parents do more at home with their kids or hire tutors to ensure that their children are working at roughly NC L5 ability to have a good chance to pass the 11+.
The reality is the government has now declared that they want schools to record how many pupils achieve NC L4b - which they now deem is the appropriate score to be 'senior school ready'.
The other reality - is that puberty & just being a teenager can be a period of time when if school is a real struggle or you fail to 'get' what the teacher/ your classmates are going on about - there is a great tendency to just 'turn off'/ 'drop out'.
So perhaps the question to ask - is would it be helpful if we actually caught them whilst they were young and sent them on from primary to senior school working into NC L5 ability?
There was a long discussion at some point on MN Talk Primary about what KS2 SATs results meant for GCSE - but basically NC L5 meant it was highly likely you'd score C or better, fairly likely you'd score B or better and there was a reasonable chance you could achieve an A at GCSE (if you worked a bit). Getting the majority to high NC L4 or even NC L5 ability - could radically change the depressing statistics for many state comprehensive senior schools.
It also may make that transition to more intensive teaching less daunting - as pupils will have the maths/ comprehension skills to cope with more specialist and demanding classes.
It's only anecdotal but there was a tv documentary (I think it was Panorama) about a school in Birmingham that doesn't expel disruptive/ problem students but deals with them in a special unit. What kept coming up was that most of these kids were disruptive because they couldn't read - cracking that meant that school wasn't difficult and they could participate.
Finally - and this is about predicting future employment directions which is tricky - but there seems to be a consistent call for a better educated - more numerate & literate - workforce. Ultimately education (just look at the history of Universal education in Britain) is about creating a nation's future workforce. So ultimately the question is not so much can teacher's do this - but may be more knowing what we do now, what do employers need in future? The needs of the employers may mean that how teaching is organised/ manned may need to be rethought.
As a parent - we got more out of paying £14.99 a month to maths factor than from St. Mediocre. DD1 scored NC L6 at KS2 SATs and with no maths homework and only two pieces of work actually shown to me briefly at parent/ teacher meetings in maths - I'm pretty vague on what was actually happening in school. OFSTED agreed that the maths curriculum needed serious rethinking. The average salary at St. Mediocre is £39K a year - obviously the Head of Maths gets more. So my question to you Cloud 2 - is what would be the outcome if well designed & responsive on-line teaching was available for each child - that could help them when stuck/ work at their pace/ and identify struggling children whilst also support high flyers. Maybe the solution to higher achievement - more one to one attention for pupils is technology. It certainly worked for us.