There are teaching aids, there are good teaching aids - and there are owls.
Take Otis Mendip, a one-year-old long-eared owl. He's a small bird - less than a foot from talon to cocked ear - but from his perch on keeper Chris Sperring's forearm, he commands the attention of a hall-full of children from Holy Trinity Primary School in Bradley Stoke, near Bristol.
Otis and Chris are the star turn of the Nestboxes into Schools project, which is enlisting children to the cause of active conservation by creating new habitats for species threatened by suburban sprawl. In such places, Chris points out, the favoured nest sites of owls like Otis - large, dying trees - are generally felled before they fall on someone's car.
Holy Trinity is the 48th school to be visited by the project, which is run by the Somerset-based Hawk and Owl Trust. So far, they've installed more than 500 nestboxes around the South-west, about half of which have been occupied by nesting birds.
Chris begins by introducing the concepts of habitats, food chains and raptor evolution. Otis scans the rows of cross-legged children, while Chris asks the questions: "Which animals have eyes at the front of their head?"
"No, but we need wrong answers."
Chris consults the owl on his arm, who blinks. "Yes. Look at Otis's.
They're huge. If Otis was my size, each of his eyes would be bigger than my head. Why are they so big?"
"To see in the dark?"
The answers, right and wrong, keep coming. The children shiver appreciatively as Otis briefly unfurls his huge wings and ruffles his feathers, reminding us that he is in fact a highly evolved killing machine.
What Otis kills and eats is a popular topic. But it's not until the assembly is over and one of the Year 2 classes is being shown how to screw together the prefabricated nestbox panels (made entirely of recycled wood, of course), that Otis obliges by coughing up an owl pellet, containing the indigestible remains of the mouse, or possibly vole, he had for breakfast.
If he had done so earlier, Chris could have used it as a visual or even tactile aid in the discussion of food chains. As it is, the children are too busy. Guided by the Trust's Keith and Linda Wall, they're learning flatpack assembly skills which will stand them in good stead for any future IKEA purchases.
By the end of the day, there will be 10 new homes for birds around the school grounds - one of them containing a tiny digital camera that will allow the children to study its occupants through the nesting season.
Year 2 teacher Lesley Clarke expects to reap the benefit of this day's activity over the coming year, when the nestbox work will become part of an overall curriculum enrichment project spanning environmental science, literacy and ICT.
For many of the children, the lasting memory will be that of simply staring into those huge, infinitely dark eyes.