Gilbert Inglefield Academy is shut for the day due to the NUT action.
Across Central Beds the only other schools completely closed are Lancot Lower in Dunstable and Arnold Middle in Barton, although the LBO understands others in the Leighton area are partially closed with certain year groups told to stay at home.
Nearly 25% of NUT members voted in the strike ballot – of those who voted, 91.7% supported strike action.
An NUT spokesman said that “teachers do not take strike action lightly” and he “wholeheartedly apologised” for disruption to parents. He added: “The problems facing education, however, are too great to be ignored and we know many parents share our concerns.”
Education Secretary Nicky Morgan said the strike was “unnecessary” and “harmful”.