I watch the teachers' faces sink as the hall explodes with huge excitement.
Feverishly flapping around the room where children are sitting at desks for the key stage 2 maths Sats... a sparrow.
The recently appointed head is wrong-footed by this special visitor. The national headteachers' qualification has no training manual for this. It covers skills for managing the staff, children, and budgets. But birds? No.
The initial strategy of asking children to ignore our small-beaked chum works as well as can be expected. But they soon want a piece of the action. Their patience is rewarded when the head returns with a child's fishing net.
They must have felt that all their Christmases had come at once. After all, they'd been anticipating a long, hard maths test and instead they get the new headteacher chasing a mischievous bird with a comical mesh weapon.
Just as the head seems to have caught it, the sparrow escapes. Needless to say, the children whoop with delight.
Another net arrives from somewhere (I don't know where these nets are kept, they've never been seen before), and now we have the head and deputy, combined salary pound;75,000, chasing a small sparrow among rows of candidates. At this point, the Benny Hill theme tune would fit very nicely.
When the bird is finally caught using a pincer movement (proving that the pound;75,000 a year is being well spent), the staff do their best to recreate a purposeful atmosphere, but much exam time has been lost.
These children have had seven years of maths education at this school.
Their teachers have drummed in the times-tables, incorporated ICT into maths lessons, and taught a range of strategies for the four operations - adding, subtracting, multiplying, dividing.
But this year's key stage 2 Sats results reflect little of this hard work by staff, and more of the fact that it was hot, the windows were left open and a sparrow flew into the hall.
Oh, to be able to tap into the school's phone line when the head explains the dip to the local authority, "No, it wasn't my leadership, it was a sparrow."
As Year 6 teachers gear up for another slog of marathon learning with another set of kids, I offer this warning: keep an eye on those house martins nesting in the gym roof. Your work can be thwarted by the most unusual visitors...
Aaron King is a supply teacher in South Yorkshire