The school bus - which youngsters and the wider community tirelessly raised funds for - was taken from the locked school grounds between 8pm on Tuesday March 29 and 7am on Wednesday March 30.
Now the school is appealing for the public's help in getting its beloved bus back.
Head Teacher Lisa Armstrong said: "I haven't got words bad enough for these people.
"Stealing from children - can you go any lower really?
"It's horrific. We are devastated.
"The bus is a community thing and everyone contributed to the fundraising and keeping it on the road, and now it's gone."
The school is appealing to anyone who may have information on the theft, seen anything unusual - or even seen the bus - to get in touch with police on 101.
The Ford Transit bus has Lythe CEVC Primary School written on the side in blue, with the registration HJ 62 JNL.
"It was used a lot and the children went all over in it," she said.
"It was a real personal thing, everyone worked hard to get it, it wasn't just a piece of school equipment."
The minibus was officially welcomed to the school in spring 2018, being blessed in a special assembly, following months of fundraising by the school, with a Sandsend duck race, a bag pack at Sainsbury's and a pancake sale among the money-spinning ventures.
There were separate donations from the community too.
Mrs Armstrong said at the time the minibus would give the children the same opportunities as if they were in a big school in a city, instead of having to rely on public transport in a rural location.