Tony Blair has admitted that he could have "gone further" as prime minister to ensure that teachers were up to the job.
He said the quality of teaching was "an issue" throughout his time in office but added that it would take "a significant period of time" to turn things around.
His comments, in an interview with The Times, come as the coalition Government prepares to give schools the power to sack under-performing teachers in just a term.
The move, coming into force this autumn, has angered teaching unions which have warned that it could become "a bully's charter".
But Mr Blair, who quit Downing Street in 2007 after 10 years as prime minister, acknowledged that he should have gone "faster and further" on school reform.
"In terms of making sure that the standard that you set and the action that you take in respect of teachers that don't meet that standard, yes, I think in retrospect I would probably have gone further on that," Mr Blair said.
He said that introducing "innovation and change" was the most difficult aspect of any public service reforms, adding: "We did that but the quality of teaching was an issue all the way through.
"I think it will take a significant period of time, by the way, to change that."
On his record on education, he said: "My basic view over the 10 years is that we put in place a large amount of investment, a certain amount of reform, probably one can say in retrospect that I would have pushed the reform faster and further."