The huge poster – which features a model writhing out of a skimpy thong plugging an online sex service – is seen by hundreds of gawping schoolchildren as they walk to the school in Bruttisellen, Switzerland.
“It is tasteless and should never have been put there,” said a spokesman for the school.
“We have contacted the company responsible and we hope it will be replaced quickly,” said a school spokesman.
Now red-faced billboard bosses have apologised and promised to take it down.
“We chose this location as it’s on private land. We were unaware it was opposite a school. We’re going to put another advertisement over this one,” said spokeswoman Sandra Liechti.