Ofsted has told a school it cannot be rated as outstanding because pupils lack experience of "the diverse make-up of modern British society".
The "large majority" of pupils at Middle Rasen School in Lincolnshire are white British and the number of disabled children and those from low income families is below average.
The school said it was looking at ways its pupils could interact with children from different backgrounds.
Ofsted rated the school as good.
Good is the second highest rating, while outstanding is the highest.
Head teacher Melonie Brunton said: "We all know Lincolnshire is predominantly white, so for us to actually have that first-hand experience we've really got to think about how we are going to make it happen.
"One idea at the moment is to make a link with an inner-city school."
Ofsted gave three reasons for the school not yet being outstanding.
In addition to the diversity criticism, the report said pupils were given work which was too easy or too hard, which prevented them from making rapid progress.
The third reason was "insufficient opportunities for teachers to improve their skills by observing best practice in the school and elsewhere".
Ofsted said in a statement: "In terms of cultural development, all schools must teach pupils about fundamental British values including mutual respect and tolerance of those with different faiths and beliefs.
"That way they will be prepared for the future wherever they go."
Chris McGovern from the Campaign for Real Education said the school "should not be penalised because it cannot do what it's required to do".
"The problem is that this school is the first casualty of a new government policy which requires schools to actively promote understanding of minority points of view," he said.
"We are all in favour of tolerance and minority points of view, but if you are in Lincolnshire in the middle of the countryside it's very difficult to have face-to-face interaction with minority groups."