Ofsted need a serious boot up the backside when it comes to inspecting SEN provision. Too many of their 'specialist inspectors' have no specific professional expertise - I know of one signing deaf unit that was inspected by a 'specialist' who couldn't sign - the inspector had no way at all of working out how good the teaching was. Didn't stop her grading the lesson though.
There are HMI's out there who know their stuff on SN, but most of the sub-contracted additional inspectors just aren't up to it. The expectations they have for outcomes for SN pupils are shockingly low.
It sounds pretty abstract, but it's fucked my kids' education badly. We lost a tribunal for DS1's indi placement largely on the strength of the Ofsted report for the LA's preferred option. The inspectors who wrote the report for the LA's school had no expertise in the relevant SEN; they simply couldn't identify poor provision when they saw it, and poor provision is what it was. On their first visit, the non-LA professionals who support DS1 were gobsmacked at just how shit it was given its Outstanding report.
The other thing is the way that schools react to what they think Ofsted want - and their reaction rarely does kids with SN any favours. Most of the 'outstanding' schools I looked at saw us as a problem - a drain on resources, an awkward kink in the data, a distraction from the main mission of the school. At worst, their attitude forces teachers to deliver support in a way that harms the kid's progress.
We really need people like Ofsted to hold SENCOs and HTs to account. The trouble is, doing it properly takes resources and expertise that are just spread too thinly. Sound familiar?