On your son's MBA, if he is logged into his user account and logged into iCloud with his account, does this still happen? It sounds like you've got iCloud Desktop & Documents enabled for your iCloud account, and because that might also be the iCloud account on his MBA, it might explain why some documents are appearing on the desktop. I'm not able to test this for you, but it might be worth a look in the settings on your son's MBA. You can confirm on your MBP settings under iCloud whether you've got Desktop & Documents enabled.thanks again for reply and for patients with my newbiness.
the user account I set up for his school work was just a standard one
my laptop in a MacBook Pro and his is a MacBook Air, both newish and both using up to date OS.
neither of us have any boxes ticked in Sharing in System Preferences. (except for 'Printers')
Now I am noticing that when either of us takes a screenshot it appears on the others' desktop. Maybe that is the extent of the sharing, but I still would prefer if it didn't happen...
You're welcome. You can think of it like this: for any device in which you're logged into your iCloud account, you will have access to all of the apps you've enabled for iCloud. Hope you know it's OK to ask any questions about this here any time.Thank you very much again Namara (and Ruggy) , I think you have solved my problem. I unticked the Desktop and Documents box in the iCloud preferences on both our laptops and the unwanted shared screen grabs have disappeared from my desktop. I hope that's it done.
I have to say, I am baffled by the various permutations of the links between all the family's Apple devices, iCloud IDs, Apple IDs, photos stored in the cloud , what is shared , accessible to whom etc.
I have some research to do....
Thanks again!
You're welcome. You can think of it like this: for any device in which you're logged into your iCloud account, you will have access to all of the apps you've enabled for iCloud. Hope you know it's OK to ask any questions about this here any time.
iCloud User Guide
Use iCloud to keep photos, files, data, and more up to date across your iPhone, iPad, Mac, Apple Watch, Apple TV, and Windows PC, and on iCloud.com.support.apple.com