The London school which hit the headlines when its head, Philip Lawrence, was murdered as he attempted to protect a pupil, has failed its inspection.
The report from the Office for Standards in Education on St George's comprehensive is expected to say it is failing to deliver adequate education.
Publication is not due for a couple of weeks, but the head and governors have been informed of its conclusions.
It is understood that the report will praise the leadership of Mr Lawrence's successor, Margaret Ryan, but will point to failings in the quality of much of the teaching.
Before Mr Lawrence took over St George's in 1992, an earlier inspection had found serious weaknesses. Under his headship the proportion of pupils passing five or more GCSES with at least grade C had increased from 5 to 15 per cent. The latest figures show 18 per cent of pupils managed five or more higher-grade GCSEs.
Mr Lawrence's death three years ago as he attempted to defend one of his pupils from a gang of teenagers triggered a debate about school security. He was widely seen as a gifted head who had secured improvements at the school.
St George's will be the second church secondary in Westminster to be identified as failing. Westminster Church of England comprehensive failed its inspection earlier this year.
The chair of governors at St George's, Peter Clair, said he been told by the diocesan authorities not to make any comment until the report is published.
Some of the criticisms in the report are likely to be vigorously rejected by governors.