A picture of Isaac Newton hangs in the Tate Britain gallery in London. Painted by William Blake, it depicts the scientist calculating the distance between two points using a pair of compasses. The image is widely believed to symbolise Blake’s contempt for rational thought. So focused is Newton on his measurements that he’s oblivious to the multicoloured, effervescent rock face beneath his naked bottom.

Having never got the hang of slide rules or cosine tables, I’ve always liked this damning depiction of reason. It’s also a fitting allegory for current trends in teaching. Except that instead of compasses we’re holding progress charts, and most of us don’t teach in the nude.

Teaching now is all about measuring. We measure where students are at the start of the lesson and where they get to at the end, then calculate the progress they’ve made in between. It’s oddly therapeutic, like placing a piece of thread on a map to see how far you’ve walked. “Ten miles,” you mutter to yourself. “How remarkable. I think I’ll celebrate with a sticky toffee pudding, a coffee and a fag.”

But not all progress is equal. Sauntering along a National Trust footpath with a pair of binoculars is not the same as scrambling up Ben Nevis with a six-man tent on your back. If we focus on the distance travelled, rather than the altitude or the magnificent waterfalls we pass along the way then, like Newton, we’re looking at the wrong things.

Teaching wasn’t always this calculating. When I first started, it involved fewer spreadsheets and a lot more papier macirc;ch. New Labour had restored “creativity to the heart of the curriculum” and invested heavily in initiatives such as Creative Partnerships. As a result, there were more artists in English schools than in the whole of the Lower East Side of Manhattan. Many schools even had an artist-in-residence, usually a low-rent playwright with a pathological hatred of children. But it did mean that there was a real creative buzz, which is what attracted me to teaching in the first place. That and the free parking, long holidays and decent pension.

But now we’re back in the land of compasses. Like parenting, teaching oscillates between two extremes: the indulgent and the anally autocratic. We’re either naming our babies after abstract nouns (I once taught a Peace and a Summer) and breastfeeding them until they’re 16, or chaining them to inflexible feeding regimes to teach them self-control.

You’d hope that one day, for the sake of the children, we’d find some middle ground. Rather than raving about Blake’s creative “tygers of wrath” or plodding behind his “horses of instruction”, we could find a solution that combines the best of both. A stripy horse with fangs, perhaps, or a big cat that goes clip-clop. Maybe even well-structured, purposeful lessons that allow the imagination to breathe. I’m sure both Blake and Newton would approve of that.

Beverley Briggs is a secondary school teacher from County Durham, England