This is despite the fact that three more schools have been put on "special measures" in addition to the five found to be failing when the authority-wide inspection was ordered a year ago.
Lambeth and the north London borough of Waltham Forest, were targeted by chief inspector Chris Woodhead following alarm over standards. The interim finding that almost one in seven of Lambeth's schools is failing is based on inspections carried out so far.
A report to Lambeth by Mike Tomlinson, director of inspections for the Office for Standards in Education, says that "as we expected, and much against the expectations of some critics, the initial high level of failure has not been maintained".
Bruce Gill, Lambeth's assistant director of education, said he was encouraged by the report. "Schools have had a clear recognition of the good work they are doing and identification of what needs to improve."
In Waltham Forest, two more schools have brought the total number of failures to six out of 60 inspected so far.