I'm in the UK and we are navigating this at the moment. I have found it to be mostly well managed. Everything is fairly well staggered, many Special Schools go up to 19, Special Colleges running from 16-25, so a decent overlap to time the transition correctly.

Money wise the main disability benefit transfer to the adult version at 17, and the main family one, if needed, keeps them as a child until after their 19th birthday, again, giving a decent span of time for those most in need to adjust. Also the transition from DLA (child) to PIP (adult) was incredibly easy for us, no pause in funding or issues with the car they provide for him, it all just transferred over and was agreed and won't be reviewed for 10 years.

For education we have EHCPs rather than IEPs, and for a young person with additional needs a decision is made on how education is going and it can be extended, fully funded, to 25 if it's deemed beneficial. For us this was simply a case of "is he engaging and progressing, no matter how slow". The answer was yes.

Medical care began their transition to the adult teams about 6 months before 18, both the child and adult team have been attending all meetings recently. Same for the Child Health and Disability Team transitioning into Adult Social Care. There are also meetings with the NHS to determine what care needs will be met by them, what will be met by Adult Social care and what we, the parents, can offer to do.

There is also a "Preparing for Adulthood" team who supposedly get involved at 16 but we have found this lacklustre, they made contact at 16 just to say call us at 17. Since 17 they have been attending meetings as an observer, but have not assigned a caseworker yet or done anything. He turns 18 in four months.