Imagine their surprise when they received a bizarre reply from the supermarket chain reassuring them about the quality control in the corporation's food kitchens.
"We regularly invite customer panels to review product samples in our kitchens and amend any felt unsuitable," said customer services.
"We were a bit surprised to say the least," said Ms Parker. "They'd obviously just sent a standard letter. We hadn't even mentioned food."
The pupils at Kew Green prep school in Richmond had spotted an arrow pointing the wrong way on a diagram about periscopes in an optics kit. "If pupils drew a diagram like this in a Sats test, they would be marked wrong," said Ms Parker.
A Tesco spokeswoman promised the company would investigate.