The points are good but I think the language needs to be stronger, so they know you're going to fight them over this if necessary. Im procrastinating so rewrote it, maybe some ideas in here might be helpful for firming up your language. Don't apologise, the only unfortunate thing here is that you need to do this at all.
Dear [headteacher]
Re: Formal complaint (Disability Discrimination)
I wanted to bring to your attention to what, after taking advice, I believe to be Disability Discrimination (Equality Act 2010). As the school is aware E is autistic and suffers from anxiety. HOY confirmed to me on xxx date that E had enough achievement points to qualify for the Reward Trip on xxx date.
However due to E's autism the HOY felt she needed an LSA to go on the trip and said that they could not provide that. E was excluded from the trip as a direct result of her being Autistic. I note your SEND policy says 'Students with special educational needs join in the full range of school activities,’ but E was excluded because of her special education needs. She was treated less favourably because of her disability in direct contravention of government guidelines.
The lead up to the trip caused E a lot of distress, this was firstly from being excluded when she'd done nothing wrong and secondly because all her friends were going and they spoke about it a lot.
Further to this, I was told there would be a 'Reward day' as an alternative for those girls eligible for the trip who could not go for whatever reason. This was supposed to be a strategy to help E with her understandable distress and feelings of exclusion. I wasn’t informed when this was dropped so had no time to prepare E for what was coming and no alternative strategy put in place to offer her some other version of the reward she'd qualified for. Due to this late notice E became very dysregulated. The late notice triggered her school anxiety and she was unable to come into school as a direct result of this. HOY insisted she would be marked down as 'unauthorised' despite guidance for schools to mark as authorised if the absence is due to illness, be that mental or physical.
Mr P has said that if staff are unable to get E into class after 5 minutes I will have to take her home. This not only amounts to exclusion, but is also a bad strategy to manage behavior related to anxiety as it makes the anxiety worse. I am aware that only a head teacher can exclude a pupil and only for disciplinary reasons, not because of their SEN. So this plan he has put in place amounts to illegally excluding E from school. It can also be seen as Disability Discrimination under the Equality Act (2010.). E had been directly discriminated against and treated unfavourably because of her disability.
As per government guidelines It’s against the law for a school or other education provider to treat disabled students unfavourably. This includes: direct discrimination, for example refusing admission to a student or excluding them because of disability. An education provider has a duty to make ‘reasonable adjustments’ to make sure disabled students are not discriminated against. These changes could include providing extra support and aids (like specialist teachers or equipment)
https://www.gov.uk/rights-disabled-person/education-rights
There are further complaints in regards to other actions of E's HOY which I will raise separately as I am focusing here on
those things that come under Disability Discrimination.
I have faith that this will be looked into as an urgent matter given the serious nature of these issues and the resultant impact on Es education. I look forward to working together to resolve these issues.
Yours sincerely,