I somehow got onto the subject of question marks in messages with my 15 yr old DS.
He said that if one of his friends sent him a message along the lines of:
"Are you coming to the cinema tomorrow?" It would be seen as demanding an immediate answer and brusque in tone. The "friendly" way would be to send:
Are you coming to the cinema tomorrow.
Is this is nationwide thing or is it just my DS's school? Do your DCs use question marks?