Glyn Hollywell, who taught German at Elfed high school in Buckley, Flintshire, did not take any money. But he ordered two administrative assistants to keep quiet about the matter and create a second cashbook to hide any discrepancies.
Mr Hollywell, since retired, was found guilty of unacceptable professional conduct and reprimanded by a committee of the General Teaching Council for Wales (GTCW).
Damian Phillips, presenting the case, told the hearing, in Ewloe: "Mr Hollywell had a responsibility to report the matter to the head but didn't do so. Whether it was out of misplaced loyalty or not, it's entirely unacceptable."
The then head Philip Pierce, now head of Prestatyn high school in Denbighshire, was alerted to the cover-up by a "rather bizarre" anonymous letter left on a windowsill in March 2004.
Graham Casson, a principal auditor for Flintshire county council, said 19 significant discrepancies had been discovered involving pound;500, plus a pound;2,200 shortfall from the sale of school sweatshirts.
John Andrews, who chaired the hearing, said Mr Hollywell acted unreasonably in concealing the alleged theft, but took into account his 39 years'
service to the profession and the fact he had retired.
"The committee also takes into account that Mr Hollywell's conduct wasn't motivated by personal financial gain," he said.