As children turned to test paper B, they found a question about germinating mustard seeds.
"Evan has three dishes," it began in true exam-style turgidity. "He puts some paper towel and 40 mustard seeds in each dish."
There follows a picture of said three dishes.
But as the four-part question continued to quiz 11-year-olds about whether seeds need light, warmth or both to sprout, some youngsters did their own count - and discovered there were not 40 but 49 or 50 seeds in each dish.
An NAA spokesperson said: "The question explicitly stated that there were 40 seeds in each dish and did not ask the children to count the seeds in the picture. No teachers have raised this with us as an issue."