Merton College introduced knife arches in February
London Mayor's office has urged schools to install knife "arches" and introduce hand-held scanners to tackle knife crimes among the youth.
Kit Malthouse, the deputy mayor for policing, said the issue was "very sensitive" but it would "make children safer".
But a teachers' group warned of "fatal consequences" if school staff were forced to search pupils.
This year 16 teenagers have been killed in London, of which 12 were stabbed.
College of North East London in Tottenham was among the first colleges to install knife arches in 2006 while Merton College in Morden introduced the scanners this February.
'High risk area'
Mr Malthouse said: "In every situation where we are using scanners we recognise the need to be very sensitive about their use.
"And schools is one of the areas where we think we need to be extra sensitive. In principle do I think it will make children safer, as a parent in London I would say yes."
John Troake, headteacher for Haling Manor High School, said: "Politicians constantly focus on what's going on in schools and seem to ignore the 19 hours the young people are out in the society."
The National Association of Headteachers' (NAHT) said: "Installing metal detectors in schools would result in staff having to challenge pupils suspected of carrying weapons. This is a high risk area which could result in fatal consequences.
"This new power should not be implemented as most school staff do not have sufficient skill, knowledge and understanding to reduce risks to an acceptable level."
It added that safety of staff as well as of students was "paramount" and said schools needed to develop a plan with police to tackle youth crime.