Twinklebum your job isn't deciding whether he qualifies, or what rate he qualifies for. That is for the decision maker.
Your job is filling in the application form to the best of your ability, detailing the day to day care needs that your son has as a result of his disability.
You may, as a parent, see the criteria and think 'my son fits the description for low rate care/mid rate care/high rate or low rate mobility/high rate mobility.
You may, as a parent, decide to emphasise the areas you feel your DS qualifies in, to the Decision Maker.
But you do have to have in mind where you are heading, as justabout says, so that you can ensure that you are providing enough detail.
Did you use the Cerebra guide for DLA? Did you get any help with the form?
You need, at this stage, to look at the detailed reasons for refusal. Then compare their reasons with what you know of your DS.
Keep a diary, note down every time you have to say something to direct, calm, guide, or assist your DS.
Note every time you have to intervene to protect him. Alternatively, if he is passive, note down every time you have to stimulate and encourage him to do something.
More crucially, really think about what would happen if you didn't do it.
Remember at every stage, that your DS will be being compared to a 'typical' child of his age. That is to say, that all 7 year olds need some assistance with hygiene. What you have to show, is how the assistance that you give your DS is in excess of that of a typical child of his age.
Typical, in this situation, is 'not exceptional'. So they couldn't say 'well a very immature 7 year old would still need....', they have to use the benchmark of an unremarkable 7 year old.
You also need to demonstrate that everything you do is because of his ASD. So explain why he requires this assistance, and what would happen if you didn't do it. Even if it is as vague as 'if I didn't do this, I would notice his stress levels rise over a period of 2-3 days, and he would start self-harming'.
You can do a paper appeal, but the success rates are MUCH lower than with an in-person appeal.