Black teachers in London schools are "under represented" and endure racism in schools on a "daily basis", a study by the Mayor's office said.
The study says black teachers and students face racism
The number of new black teachers in 2005 rose by just 0.3% since 2004, the study, Black Teachers in London, found.
Lack of support and limited career growth were cited as reasons for many black teachers leaving the profession.
The number of black teachers is disproportionate to the number of black pupils in schools, the study revealed.
Hackney, Lambeth and Southwark boroughs have the highest proportion of black teachers, 16% to 18%, but in contrast Lambeth and Southwark have nearly 50% black students.
'Reflective teaching staff'
In a statement Mayor Ken Livingstone said he was concerned about the under representation.
"Two years ago we underlined the need for more of London's teachers to come from minority ethnic communities to reflect the fact that more than a third of London pupils come from minority ethnic communities.
"But at the current rate it will take far too long to have a truly reflective teaching workforce."
In 2003, the Aiming High Initiative was launched by the Department for Education and Skills to encourage students from ethnic minorities to perform better.
The number of black students achieving good results at GCSE has gone up since then.
MP Diane Abbott said black teachers have a vital contribution in this.
"The recruitment of black teachers remains an important issue and I believe they have a vital role to play in helping black children succeed," she said.
The report also came down strongly on racism faced by black teachers and students and said it needed to be "forcefully changed".
Respondents to the study said they need an independent support network and professional guidance on development opportunities.
The report will be formally released by Mr Livingstone at the fourth London Schools and Black Child conference on Saturday.