It does seem like he's had a rotten week here, but for the sake of a different viewpoint let's play devil's advocate...
I would assume that at 14 he's not supposed to have unsupervised contact with the children, and that's why they weren't happy about the Rock, Paper, Scissors situation. Whether that was made clear to him or not is another matter.
The bowling? Perhaps they viewed this as mucking about when they'd given him a job to do?
The staff room is presumably adults only and he is very much a child at 14. I can understand them not wanting him in there potentially overhearing things, especially when he has a sibling at the school.
The mundane tasks? What can you do, realistically, as a child in a school environment? Work experience often means shitty busy work. Which leads us to...
Bad attitude/communication. Could this be as a result of his expectations and the reality of the placement being so far apart that he was fed-up/miserable all week? Again, not his fault, but a textbook reaction from a miffed young teenager.
The lack of feedback? You say he wasn't given an induction or guidance...I guess it's equally possible that whoever was 'responsible' for him day-to-day was similarly unaware that they were supposed to be delivering coaching/feedback.
I'd certainly be talking to his school, not the placement school. Firstly for more specific feedback that he can action and secondly to make sure they're aware of what his week entailed. If they were aware I'd want to know why it wasn't made clear ahead of time and if they weren't, they need to communicate with the placement school and either agree on a more beneficial framework or stop offering placements there.
Anyway - Perhaps a bit of a life lesson for him. Are you able to arrange some work experience independently at weekends or during the school holidays?