Every now and then I am astounded by the level of ignorance that my pupils display. Now, I know this is purely subjective, as what I'm really astounded by is the level of ignorance about the things I know, but surely there are words, places and people that everybody knows.
All in the matter of a few days a group of fifth years shocked me with the uncomprehending stares, behind which lurk minds landscaped by laconic tumbleweed in a windblown desert.
On Monday they tell me they have never heard of Napoleon Bonaparte.
On Wednesday they shake their heads doubtfully when I mention the English Channel.
I point to the huge map of Mother Europe on the wall. No, never seen that little sleeve of water before.
"Look! England's very close to France down there.
"That's Kent and when you take the ferry from Dover you can actually see France as soon as you leave the harbour."
Can't be right, they retort. I assure them that it is.
On Friday we come across the word 'furtive' in a text. What does that mean? No one knows. Maybe the Polish kids know -- their English tends to be good and I've actually seen them reading books in the school library. No, they haven't come across 'furtive' -- yet.
So I tell them that it kind of means to move in a sneaky way so that you won't draw any attention. Fast forward to Monday.
'Hey guys; what does the word 'furtive' mean?'
Blank faces all around. I'm fit to burst a blood vessel at this stage -- I want to set off the fire alarm, but I'm not sure I can make it to the corridor without having a heart attack.
Instead I tell them that they really ought to think about what they have done in class after they leave the school building -- that's what school is for, after all.
They look at me as if I'm mad. They're thinking: heard that before and that's a totally unreasonable suggestion -- as if!
This all leads me to the conclusion that what we have lost in the past 20 years is a common culture that provides us with a common 'general knowledge'.
Back in the late 1990s the kids used to scrawl Oasis, X Factor and even Tiger Woods on our desks because that was all that was out there at that moment.
Nowadays kids no longer watch what they call 'appointment TV' like in my day when we all tuned in to Top of the Pops at 7.30pm on Thursday and the next day at school everyone knew what song was number one in the charts.
Now people check the schedule and store it on the hard drive, make a personal choice to watch something online or get a DVD.
We no longer all watch TV at the same time.
What used to be a shared culture has been fractured by technology and an Irish celebrity chef is recognised before the man who shaped modern Europe.
Eh, that would be Napoleon.