Unless a child has some degree of special needs they should be able to dress and undress themselves quite competently by 4 years old.
Mine had to wear lace up shoes and ties at prep prep, the last 10 minutes of the day was spent teaching this and helping each other, After a week they could all do it.
This is what the local state nursery require for 3 year olds.
Encourage your child to be as independent as possible. It is very helpful if he/she can do these things at home in preparation for the demands of a busy nursery class:
Remove coat and hang it up.
Go to the toilet unaided
Wash and dry hands.
Put on own shoes.
Dress and undress.
Use a tissue to blow own nose.
Tidy and clear away toys.
Share with other children.
sandyball My sister and I call them" coathanger" children, they stand with their arms out waiting to be dressed. As a school nurse she sees it a lot.
My nephew was like this as he had a philipina nanny who did EVERYTHING for him, drying between his toes at 7, and wiping his bottom!
OP I think the school are being put of order. I take lots of little ones to prep and pre prep, none of the mums, childminders or nannies are ever have to stay and help. The girls are expected to do it themselves, some were only 4 in August. It is amusing though when they come out in the first few weeks, you know which days they have had PE, socks on inside out, collars tucked in, tunics askew! They soon learn.