They damaged a padlock on the gates at Kettlethorpe High School between midday on Monday and 7.30am today (Tuesday).
The crooks then stole a small dumper truck and a digger, which were parked on the school grounds.
The vehicles were being used to resurface the school’s tennis courts and build a new fence.
Site manager Steve Haswell said: “The construction company found the vehicles had been stolen this morning.
“There are lots of tyre marks around so we don’t know if they drove off in the vehicles or drove a truck in and loaded them onto it.
“The work has been going on since the start of summer. It is nearly finished so I don’t think the work will be disrupted too much.”
West Yorkshire Police are now appealing for witnesses.
Anyone with information should call police on 101 or Crimestoppers anonymously on 0800 555 111, quoting the crime reference number 13150333172.