My DD (now 16) has moderate LD's, Autistic tendencies, S&L issues.
She has just completed work experience and will be going to collage in September having gained the equivalent of GCSE's (to give you an understanding of were she is up to).
Until she could safely have a phone (and even then), I put her name, address and contact numbers, an explanation of why she wasn't communicating, in at least two pockets/bag etc.
This allowed her a greater level if freedom, I didn't have to shadow her.
She also appropriately played out with her sister, but we put safety measures in place, in different scenarios.
I spent a lot of time teaching her what to do if she was lost and deliberately took her on public transport.
Personally, I think it's sensible that the school is doing this and your DS might not like having to always hold a member of staffs hand, he might like the increased Independance that having these measures can allow.
He will be in a whole different Senario than being out with you, in a familiar place.
It's sounds to me that the school are just expecting the unexpected.