This is absolute rubbish and very depressing to see a thread on it.
Firstly, there is a difference between being on the special education needs register and having a statement.
Secondly, Special Educational Needs are not the same as Special Needs. It means there is some reason why they need extra help to access learning in the classroom.
Thirdly, there are just a billion reasons why children need to be on the SEN register. There is absolutely no way ofsted would look at the number of children on the SEN regsiter and assume poor teaching. There is just no correlation at all.
Schools put children on the SEN register as they see fit. Most schools would do this for good reason. But obviously there will be some schools who are trying to play games with statistics. Some of these schools may put children on the register who don't need it - and some will do the opposite. Depending on what statistic they're tying to game.
There is a huge variation in the quality of individual teachers and individual schools. And it stands to reason that some kids will have been failed by bad teachers. But that is the same in absolutely every job.
Often the best schools have the most kids with SEN there - because they are actually good caring schools which can cope with a wide variety of pupils. Whereas schools with good league table results have often done that by driving away SEN kids - and generally have far weaker teachers and pastoral care. Anyone can get good league tables if your intake are rich and the kids get tutors etc....
My advice to anyone who is choosing a school - be very, very suspicious about a school which has a low number of kids on the SEN register. It could well be because they were unable to cope with them and they all chose to leave. (My old school can't be the only school to have done this...)
Plus - I'm sure you really hope that if your child was having difficulties the school would a) notice it and b) do something about it. A school without many kids on the SEN register may well be failing to do these things.
OP - I hope you never have to experience the stress and worry and anxiety of having one or more children who have special educational needs. It is not something I would wish on my worst enemy.