At the heart of this debate is the issue of grade inflation, and the dumbing down of the curriculum which his critics lambast him for. It's not that Johnson ignores this possibility -- he readily admits to it himself -- but he offers a more optimistic position than his critics can stomach.
In exam-crazy Singapore, our 'A' Level curriculum in math and the sciences makes my own head swim. As it is, our primary school math already makes me stare and blink blankly at the questions the little tykes have to work out. The 'A' Level timetable is a marathon sprint event, the kids being swamped with so much of revision, homework, tutorials, remedials, consultations, it's no fun being a JC student any more. Academic rigor we have... almost to the point of mortis, if you ask the kids themselves.
But curriculum and exam results don't impress me. They're a poor indication of intelligence, biased as they are to a particular kind of left-brainedness. If I were taking my 'A's in JC today, I'd probably be curled up in the corner of a darkened room awaiting my next sedative shot by the time I got to my prelims. It's the fact that our kids actually survive the stress we put them through and are still able to move on towards their next step in life that I respect about this generation.
I'd like to think our kids are getting smarter, at least for for the simple reason that more kids than ever are getting access to an education. Sure, they may not all be able to handle a chemistry paper set in the 60's like some of Johnson's respondents were suggesting, but that's because the kids taking their 'A' Levels in the 60's were truly the creme de la creme of their cohort, both intellectually capable as well as being able one way or another to finance their further studies.
Besides, the 60's generation didn't have access to electronic secondary memory systems (Google, Wiki...) they had no option but to store everything they learned within their own biological primary memory. In that capacity, they were limited to only what they had memorised regardless of how much that might have been. So perhaps they might have been smart in that sense but they could only deal with information stored within the realm of their own heads, and only if they kept updating it manually.
Public education made intellectual development available to pretty much everybody. That might have meant a bit of levelling out of the curriculum towards an average, certainly not as high-level as what it might have been before, but a drop from the top meant a raise in the smarts of everyone else.
And where Johnson's critics pooh pooh computing and the 'net, it's because they see these newfangled developments as inert, inanimate objects rather than the living network of streaming information that actually runs under the hood that our kids are tapping into. The only problems we're facing on this front is the immediacy of access due to the clumsiness of our current interface technology, and the literacy skill that we need to develop in our kids so they can navigate it.
When we figure out these speedbumps on the highway of digital intelligence, we can do away with our archaic biological memory based exams and set exams that are not just open-book but open-'net. They'll be answering exam questions through the usual Wiki and Google, but also through online forums, chats and other forms of interaction with real people (friends, strangers, idiots and experts alike) interactively and collaboratively. That'll be more realistic to the digital age. After all, what's the equivalent of an "exam condition" in the real world today? A power failure or system crash, I suppose, which doesn't happen too often to be a concern.
What if Bolt runs under 60's conditions, the critics posit? Would he still run 9.58 secs? The answer is, it's not the 1960's any more. Times have changed and we have changed with them. We have created the conditions under which running 100m in 9.58 secs is possible, and that is the story of human progress.
Are our kids smarter today? I don't know if we have got the conditions for intellectual Usain Bolts to exist just yet, but on the whole our kids know more and have access to even more useable information than their parents did and way more than their grandparents ever did. That's a good enough yardstick for me.