Last week I took my family for an evening meal in the French cathedral city of Albi in the Tarn. It was still warm and we sat down on the outside terrace and soaked in the atmosphere of the birds singing, the diners chatting and the lovers cooing. Except, that is, for the table next to us where a family had in its number a daughter who did nothing all night but play games on her phone.
The mother and father spoke in Gallic animation with another child - but how rude and disrespectful to her parents, who did not appear impressed, and how disrespectful to herself that the girl could be so bad mannered and brazenly so.
It was, sadly, not a unique situation and I draw attention to the incident to point to the difficulty that teachers face in dealing with the use of mobile phones and social media in class. How are teachers expected to deal with such distractions when parents are unable or unwilling to deal with it in the familial setting?
The public's attention has been drawn to the growing phenomenon by the publication of a Scottish government report which revealed that, second only to "running in the corridor", instances of mobile phone abuse are the most common form of indiscipline faced by teachers.
Immediately the "simple" solution of banning phones in the classroom, if not the school, was proffered, but I fear that is not as simple as might be supposed in state schools, with their unavoidable political pressures to accommodate repeat offenders of low-level indiscipline.
Phones are not just for talking; they can text, they can Tweet, they can photograph and they can film - providing a window to the world of the classroom in real time. The potential for disruption, for insulting staff and humiliating other pupils is limited only by the battery life.
Introducing signal blockers would be expensive, especially at a time of scarce resources, and they do not prevent phones capturing images.
The use of phones in school cannot be dealt with by guidelines or rules alone - what is required is greater respect for teachers and heads with acceptance that their word is the law in a school - but more so, we need society to develop a sense of decorum about the use of phones in all their guises.
Quiet railway carriages should become just that and no-phone zones in schools can be made to work. But unless parents are encouraged that modern manners sometimes require phones to be left behind then the problem facing teachers is only likely to grow.
Brian Monteith is a political commentator.