YOUNG children in Croydon are falling behind those in London and the rest of the country according to a new progress measure.
Good Level of Development (GLD) scores see teachers assess five-year-olds in 12 key areas including communication, physical development, literacy and maths.
According to the first batch of results, following assessments last summer, Croydon children are below the national and London average in every area.
Nearly half (44 per cent) of those assessed by their teachers were found not to have good development in literacy and one in three were not at the expected level in maths.
At a scrutiny meeting on Tuesday night senior council officers said they were not unduly concerned by the results.
Paul Greenhalgh, executive director of children, families and learning, said: "The first year of a new methodology doesn't, in itself, concern me.
"What I would be concerned about is if, in the second year of the methodology, the picture that happened last year was continued.
"But given that under the previous methodology Croydon did reasonably well, and in terms of the gap between children from deprived households and the rest, we were doing better than the national average, our hypothesis remains that our teachers in Croydon were possibly over cautious."
Mr Greenhalgh said guidance was issued to teachers before the assessments were undertaken.
He added that by April each school will have received a moderation visit and, as a result of that work, he "expects the pattern to be different".
He added: "Just based on one set of data, with a new methodology, there are too many questions for this to register as a significant concern."
Heathfield councillor Jason Cummings said he was sceptical that the results were down to teachers in Croydon doing anything significantly different from elsewhere in the country.
But he was reassured that advice had at least been issued before the assessments were done.
The GLD scores replaced a previous assessment, based on a 117 point scale - of five-year-olds at the end of their Early Years Foundation Stage (EYFS).
It was introduced in September 2012 following an independent review by Dame Clare Tickell. The first assessments were done last summer.
In Croydon the percentage of children judged to be making making good progress in their development was 46 per cent, below national (52) and London (53) average.
