Police are investigating two thefts from The Deepings School.
A man was seen walking into a bike shed at the school, in Park Road, Deeping St James, at around 2.30pm on Friday, November 25.
He removed a blue Diamond Back Sync 4.0 bike, which has racing handles and a black seat.
The man was said to be wearing a dark hoody - possibly navy blue, black jeans or trousers and bright blue Nike trainers with white ‘swoosh’ logos.
Police said he rode off out of the school car park and then went down Linchfield Road.
Anyone with any information regarding the incident should call Lincolnshire Police on 101, quoting incident number 295 of November 25, or Crimestoppers, anonymously, on 0800 555111.
Officers are also investigating the theft of a Pandora bracelet which was taken from a school blazer during a PE Lesson at the school on the same day.
The bracelet is said to have had four charms and three rings attached to it - including a dog bone charm, a heart charm, and a birthstone charm.
Anyone with information regarding the bracelet theft should call police on 101 and quote incident number 292 of November 25.