Remember that Time is Money. He that can earn Ten Shillings a Day by his Labour, and goes abroad, or sits idle one half of that Day, tho’ he spends but Sixpence during his Diversion or Idleness, ought not to reckon That the only Expence; he has really spent or rather thrown away Five Shillings besides.

Benjamin Franklin

There are those that would have it that opportunity cost is a concept so complex as to be impenetrable to anyone other than highly trained economists. Opportunity cost, the idea that making a choice precludes another option being chosen, is a threshold concept. It’s hard to get your head around all the implications but once you do, it changes you. You can never think about choice in quite the same way ever again.

Here it is in a nutshell: The opportunity cost of a choice is the value of the best alternative foregone, where a choice needs to be made between several mutually exclusive alternatives given limited resources. What this means is that if you have two choices – go out for a drink (A) or stay home and mark students’ books (B) –  the opportunity cost of going for a drink, is the time and money you spent on going out plus the value of having stayed home and marked. A traditional cost/benefit analysis doesn’t give you the true picture. The true cost (C) of a decision is A-B=C.

When calculating the desirability of a course of action, how often do we take into account the value of the value of the best alternative? For every decision, there is an explicit and an implicit cost. The explicit costs are obvious ones: the money, time, staffing expended in making the project a success. The implicit costs are the hidden costs represented by the failure to allocate precious resources elsewhere.

So our simple equation, A-B=C can be better expressed as True cost = Explicit value – Cost of chosen option – Implicit value of foregone alternative. But how is this calculated? To return to our example, going out for a drink on a Tuesday night might result in accruing units of enjoyment. From this, we have to subtract the cash we’ve spent on drinks and the enjoyment of ploughing through a pile of marking. Maybe some of you enjoy a few hours of marking, but for most of us, the night out is a winner in terms of raw enjoyment units. But, hang on, what happens on Wednesday? You’re hung over and you’ve not even looked at those increasingly dog-eared exercise books! Tuesday evening might have been fun, but Wednesday is a bummer!

The most precious of our resources is time. Time is always finite. You can only spend it once and once it’s gone, it’s gone. Now you might very want to argue that going out for a drink is time well spent, but opportunity cost really comes into its own when considering the time we spend working. The cost of every decision we make in school is Explicit value – Implicit value.

That’s the value of marking books? On the plus side we add the sense of virtue felt on clearing the backlog, the gold stars we might earn from management and the positive impact on our students. To the deficit column, we must add the potential benefits of doing something, anything, else. You could have been planning, phoning parents, doing admin, playing tennis, seeing your own children, or having that night out with friends. The point is, time spent doing x is time you cannot also spend doing y. Unlike money, time can never be earned back. Once time is gone, it’s gone forever. Let’s say that marking a set of Year 8 books, which you find soul destroying, has the arbitrary value 50 in terms of student achievement (whatever that might mean). Then let’s say that planning a really fascinating lesson has a value of 40 and getting an early night has a value of 10. That would mean that the opportunity cost of marking minus the foregone advantage of planning and sleeping long was neutral. Worth it?

Another example where we would do well to consider opportunity cost is curriculum planning. Because time is finite we can’t study everything. This means you have to make a choice. You might have a stock cupboard full of Robert Swindells’ novel Stone Cold, but the opportunity cost here is the value of studying Stone Cold minus the value of studying all the other novels you could possibly choose. Now, you might really like Swindells, but is he a better writer than Chaucer, Shakespeare, Austen or Chesterton? And even more important, whatever the value in terms of enjoyment of reading Stone Cold (I’d say it was nugatory, but I’m biased) what’s is the cultural capital of Swindells’ teen page turner? To what extent is it going to help build students’ vocabulary? What will it teach them about history, society and human nature? Is it really the best choice? Or just the easiest? Maybe you can justify Stone Cold. Maybe you’d be happy for your own children to spend precious curriculum time reading something of little intrinsic worth. The cost here seems to be engagement (Although again, I’d want to argue that while teen fiction might be more accessible, it isn’t as much fun as getting to grips with something of depth and richness like Armitage’s rip-roaring version of The Odyssey or Heaney’s majestic ranslation of Beowulf.) minus cultural capital. Whilst every book maybe worth reading, curriculum time is too scarce to waste studying works of little depth or relevance beyond their own shallow milieu.

The cost of Learning Styles is not just the sunk cost of time and resources spent on VAK questionnaires, it’s all the time and thought you could have invested in something better. And, maybe most crucially, the cost of doing a ‘bit of both‘ with regards to enriching students’ knowledge of the world or trying to teach them transferable skills is that you will do neither as well as you might if you expended all you time and energy on the one which actually made the most difference to students’ life chances.

And to return to marking – maybe you’re convinced it’s a great way to get students to achieve and you feel great for doing it. But here’s the kicker: who’s to say marking is worth more than planning? The real cost in terms of students’ achievement might be impossible to accurately calculate. As I point out here, giving students feedback might, in some cases, be detrimental. And even worse, as Jo Facer has argued, the cost of drudgery might be teacher burn out. What is the opportunity cost of teachers leaving the profession?