Why are comprehensive schools allowed to have selective Sixth Forms?

The policy of entry requirements is no more selective than life Im Afraid. Universities will require certain grades and saying you have had poor teaching in the past, will not result in lower offers. When firms look at job applications, one of their criteria will be GCSE or A Level or degree grades and they will bin those who don't meet their threshold requirement. They won't give special consideration to those from certain backgrounds or even dyslexia I'm afraid. It's the reality of the world.
After the early entry with no resit option is dealt with, your daughter will have to compete with everyone else. I know we don't like to think any doors are closed to our children, but as they get older we and they have to understand that the world is a competitive place. Her exam results will be the things that are seen first by educational establishments and employers. If she under performs in exam conditions, it will disadvantage her in many situations, which might not be right, but you do have to accept it is the system we live in. Sorry if it sounds harsh.
If you believe she has the ability to achieve good grades at A level in an exam, which will be good enough to get her to the next stage, perhaps go to the other establishment which will take a B. you could always ask for statistics of the A level grades achieved by those who started with As and those who started with Bs.

GCSEs are intended to be a comprehensive qualification, suitable for all 16yos.

A/A* identifies the top 25% in that particular subject; these are the students who'll be able to do well at A Level. The school will be under huge pressure to maximise its A Level results, so there's no incentive for them to offer a place to a

I must say it was a surprise to me to see how selective our comprehensive's 6th form is, but when you chew over all the arguments I think it is reasonable that it is like this, even if at times it seems cruel.

However I think if nothing short of an A at GCSE is good enough, you have to wonder whether the our current GCSE system is a bit wonky. For what its worth, I got a B's at GCSE in the seventies and there were no questions asked about doing the A level in that subject.

I can see what you mean. Most pupils don't really benefit from taking exams early. Many will achieve a grade lower than they would a year later. The only reason I can see for it is they are trying to relieve the pressure of pupils taking so many exams at once.....and this is caused by putti g them in for too many GCSEs (most selective schools will only do 9 GCSEs because more than that are of absolutely no benefit. Better to get 8 or so good ones than more mediocre ones). That issue is for another thread though.
However you are right that if they are put in early,especially for a core subject,they should be given the chance to retake, (if there is a sense of underperformance) especially if they have been promised it.
However, I still think the evidence shows that it is important for schools to set entry requirements for Academic A level courses, because it helps no one to have students doing them who have no real chance of success. Whilst it seems at odds with the experiences we as parents had doing A levels successfully from Bs and Cs at GCSE, these days such GCSE grades are not sufficient for A level success in subjects like maths. The jump up is great.....partly due to topics which used to be In GCSE having been cut....again another thread topic.
Ability in the subject is one thing to consider when deciding to do A levels, but so is being able to manage in exams.....because that is how the grades will be given at the end. It won't matter if you are good in class or in non timed conditions, exam performance is what will matter.

Whilst I agree that there's generally a case for restricting A level entry to those with a decent chance of success, in your DD's case I'd kick up an enormous fuss, because her B grade is not a reflection of her abilities, it's a consequence of the school's decision to put her in too early and then refusing to let her resit as per the original plan. I hold no brief for Gove, but I'm much more shocked by the school's decision to ban retakes that would benefit their pupils just because there's nothing in it for them. Does this strike nobody else as a grossly selfish dereliction of duty?

I understand your problem with this. However, if the sixthform only offers A-levels, what is the point of setting students up to fail? The school will have based their entry requirements on the profile of candidates they believe can cope with A-levels. It does seem a bit strict, and perhaps you could argue an exemption for your DD. However, the jump for GCSE to AS is a major step up, and there is no point letting lots of students in, only for them to fail all their AS exams.

I went to sixth form at a comprehensive school, and the grades needed to get into sixth form were fairly lenient (5 A*-C grades including English and maths, however if one out of English or maths was lower than a C, you were allowed to resit it in October). However, the requirement to do individual subjects was usually a B grade as a minimum in those subjects, with an A being asked for in the sciences and maths. So, in reality, someone who got 5 C grades would be unlikely to continue on to do A-levels.

People often still failed and dropped out in the first term, and were often put off education entirely, when a BTEC at college might have been a better path for them. I think it's probably the best thing for students to be made to consider other routes than A-levels and university, as it's really not for everyone.

If she gets an A in lit, I am sure you would be able to make a good case for her to be allowed to do English A-level.

The school DD attends is also proposing to redraw its catchment area to exclude the poorest area of the borough

That may well be a breach of the Admissions Code. Make your objections known to the consultation. If they still go ahead you should refer the matter to the Schools Adjudicator who will decide whether or not the school has breached the Code.

Our local CofE school makes a big thing of all joiners in year 7 having to have letters from the vicar yadda yadda. Kind, Christian, inclusive yadda yadda.

Then kicks out anyone who doesn't get an A and allows the local high achieving heathens from independent schools to join at sixth form .

Agrees with everything Chocolate Wombat has said. Unfortunately getting extra time at school does help the person with dyslexia to pass but if they end up in an admin job or even in teaching they will struggle with paperwork and whilst adjustments will be made to support them they will still be expected to get the same amount of work done as their colleagues. It's a tricky one all round.

Blame the League Tables. All the reasons you might have picked that school are now being used to exclude some children.

That is the reality of a results driven culture.

I'm sure you are right that the extra time doesn't totally level the playing field. It is an attempt to go in that direction.

The sad reality is that we live in a country where exams are the key way of assessing people. Those who struggle in an exam environment don't perform so well. GCSE exams are a good predictor of A level success which is why schools use the, as entry requirements. The system might be wrong, but universities and employers use those exam based grades as a basis for judgement, so we do have to work within the system. More children are probably suited to undertake the study required and understand the material than are able to perform in the exam....but that is the system, and we are moving closer to it, with the reduction in coursework.
If you are sure A level English right for your daughter and the exam wouldn't be a big issue for her, then the idea up thread of re sitting privatelty the GCSE is a good one. If she was so close last time, then she has a good chance of getting the grade. Good luck.
There will always be borderline cases, but schools need entry requirements in place so that broadly the right people do the right courses. There are always grey areas and it sounds like your daughter might me one. Best of luck.

How about re entering your dd for the exam as a private candidate in the summer? Her CA would still count towards the final grade (though not sp and li). If she improved her result to an A, would school accept that? If it's the school I think it is, the recentlyish opened church/LA academy down the road has a good 6th form from what I hear and doesn't require church attendance.

No extra time does not level the playing field, it's a small and for my DD1 useful apology for the 'unfairness' she has suffered since reception.

If DD1 lived in a world where exams were aural she'd get A* across the board.

If she lived in a country with a more phonetic language or if her schools had decent dyslexia support she'd way better.

Extra time is a feeble apology for the shocking amount of effort it takes to get dyslexia recognised and appalling lack of help available.

It's a tiny recognition of the huge waste of talent that results from one size fits all written exams being the only way to measure a persons intelligence and employability.

DD wants to be a research scientist to work in a field where any written piece of work she does will be carefully crafted on a computer, the technical terms looked up if she's forgotten how to spell them.

No one will care about her B/C in English they will care that she has a quick interested brain, a hardworking nature and a deep love of working out how the world works.

Should have added that those with recognised SEN get extra time in exams etc and may have some allowances made for them in termsnof entry requirements. However they to ably had extra time at GCSE too, so in that sense their GCSEs have been boosted up to create a level playing field.
A levels are becoming more exam focused and less coursework focused. This doesn't suit everyone and people who panic in GCSEs may do it in A levels too. It's just the academic nature of A levels that means an academic approach, which doesn't suit everyone.

Good luck Op in finding the right place and course for your daughter.

If a sixth form only offers A levels, it needs to be selective. A levels are not suitable for all students and never have been. The school or college would not be doing kids a favour to let them start A levels when they don't have a chance of success.
Uni courses are increasingly competitive. Good grades at A level are needed to get onto the best courses at the best places. With the high level of debt incurred and high graduate unemployment, more people are thinking carefully about if Uni is the best option for them. Spending 2 years to achieve very low grades or fail is really not a good use of time and schools know that.
Schools which offer a range of vocational or other courses may be more open access, but there are often some requirements for these courses too.
It is not unusual these days to require an A at GCSE in the subject you want to do at A level. People with Bs may be let onto some courses, but statistically their chances are not good. With a C at GCSE in that subject, you really have no real chance of a good grade.
It seems harsh, but people need to think really carefully about if A levels are the right choice for their child and certainly about their subject choice. Schools are interested in league tables, but also the interests of their kids and pushing to start with grades below the requirement isn't usually doing kids a favour.