Parents of pupils at the Stephen Freeman county primary school in Didcot, Oxfordshire, have been told their children will have to to resit their Sats (standard assessment tests) in maths and reading.
About 59 year two children took their Sats five weeks ago. Now 30 who achieved above-average level three grades face another afternoon's testing early next week.
At a meeting yesterday to explain to parents what has happened, Tony Price, headteacher at the 400-pupil school, said: "Over 50 per cent of the children have scored level three in both subjects. This is abnormally high and Oxfordshire County Council education authority has the discretion to retest."
Mr Price added: "I do sympathise with the children but my hands are tied. I also sympathise with the parents' anger and my own staff.
"It was a heated meeting but I think that once the parents calm down they will do the sensible thing."
A spokesman for the council's education department defended its move yesterday. "We noticed that the results there would not be what you expect," he said. "They were not in line with both the county or a national level - they were out of kilter.
"It may be that the children are exceptionally bright or have benefited from some wonderful teaching. We are not prejudging them, we just want to see what happens.
"It is not unfair on the children but I agree that it is unfortunate. In an ideal world we would not do this."
He said the National Union of Teachers and the National Association of Headteachers had been consulted and supported the retesting.Reuse content