I've another friend who is refusing to get son tested for dyslexia as she doesn't want him labelled and 'it won't make a difference' to know.
At last school my DC went to it wouldn't - in fact people who did get tested outside school found it was then used as a limit on the DC and what could be expect of them. I spoke to several parents who found this and it didn't bring any extra support.
It's rife in our family - so not unexpected so we're not looking for excuses and despite their issues they are doing well now.
We've moved and are waiting to see what their new school take is and then the secondary's while offering support at home for the two I think have problems. We have time before we get to the exams.
We've experienced teacher at the last school desperately wanting our DC to have extra support but the SENCO deciding that they weren't struggling enough at that point - then nearer sats it being a massive issue - or being told they grow out of it.
Also experience very poor interventions - one to help reading with DD1 was to get her to read a list of words faster and faster with TA so she was missing lessons but it had no impact on her normal reading speed and she would still read the same words wrong in another context.
Ironically that school was very good with ADHA and autism in children - not so hot on dyslexia and dispraxia.
I'm surprised a diagnosis is need to put some support in place - it was common in their last school for DC to have support for a bit then not need it any more.
I assume you've done a meeting with teacher and SENCO saying this is the list of concerns in our x number of years of experience this indicated these could be possible causes so would like to get diagnosis or them ruled out - this is support we can offer however we'd like to offer x but can only do this with diagnosis - or process started.
I do know some parents who were initially very hostile to idea there were underlying problems - they often have well meaning people round concurring with their denial. However the professionals round them - have been sympathetic and gentle and persistent and have got them though diagnosis at which point they'v access so much more help and support.
I think judging them while they get their heads around it would have been counter productive.