Ofsted has called for the Department for Education to record data on pupils' managed moves in the same way it does for exclusions.
The inspectorate warned that there is little evidence on how well managed moves between schools or pupil-referral units (PRUs) work out, and that nobody has a clear picture of how often it takes place nationally.
It highlights this in a report on how London schools deal with pupils carrying knives.
Opinion: Schools can kick the exclusions habit
Opinion: 'Off-rolling is unethical, inappropriate and beyond repugnant'
Off-rolling: Should schools be held to account for ex-pupils?
Ofsted said school leaders used managed moves as a response to children carrying knives more often than excluding the pupils involved.
The inspectorate said that most of these moves were permanent and to another mainstream school but sometimes they were to PRUs and could also be for a fixed or trial period.
Managed moves: do they work?
The report says: “We do not think that any single body has a clear picture, either in London or nationally, of the number of children who are ‘managed-moved’ to different schools, how long for and where to or for what reason.
"We also do not know what the educational outcomes for those children are, or whether managed moves do, in fact, effectively safeguard those children or keep them in mainstream education in the long term.”
The publication of the inspectorate's research follows claims from police chiefs and the mayor of London, Sadiq Khan, that a broken school exclusion system was contributing to a rise in knife crime.
Ofsted warned that schools do not have the resources to be able to deal with knife crime alone.
Yesterday, the chancellor, Philip Hammond, announced an immediate £100 million for police to tackle knife crime but made no new funds available to schools.
Ofsted's report questions the way in which some pupils have been excluded for carrying bladed objects in school.
It says it has heard of several examples of pupils being "manage-moved" because of knife incidents.
The report adds: “One pupil who was carrying a knife who feared travelling to and from school because he lived in another borough was moved to a school that required a different route.
"The difficulty with this type of move is that we do not know if moving the child solved the problem in the short term or for good.
“There is currently little evidence on the efficacy of managed moves.
"That is not to say that they are not effective in safeguarding children or ensuring that they continue, with as little interruption as possible, in their education.
"That may indeed be the case for many of the children who are subject to managed moves, and we know that in some cases they are used as an alternative to permanent exclusion.
"However, further evidence and research is needed before central and local government, headteachers and other stakeholders can be assured that managed moves are being used in the best interests of children, are keeping them and other children safe, and are leading to improved outcomes for the children concerned.”
Last spring the Government launched an externally led review of exclusions practice, led by Edward Timpson.
Schools minister Nick Gibb said earlier this month that the review's findings are to be "published shortly".
The DfE has said that as part of its work the review will look at how managed moves are used.
It has been tasked with looking at how exclusions are used, why certain groups are disproportionally affected, and why there are variations between regions.
