A team from Ofsted have spoken to inmates at a Kent young offenders centre following allegations staff assaulted young people there.
Officials visited the Medway Secure Training Centre (STC) in Rochester, managed by security firm G4S on Monday.
Seven staff were suspended after secret filming by the BBC Panorama programme.
Justice Secretary Michael Gove told the House of Commons he would be meeting with the firm this week to discuss the allegations.
He said the alleged assaults would be treated with the "utmost seriousness" but it would be "quite wrong" to make a "blanket allegation" against G4S, pointing out that other institutions which it operated did a "good job".
'Shocked and appalled'
Shadow Home Secretary Andy Burnham has said if the claims are true, G4S should be stripped of its contract to run Medway and other STCs.
The allegations - uncovered by Panorama - involve unnecessary force, foul language and a cover-up.
The claims relate to 10 boys aged 14 to 17.
The programme is due to be broadcast later.
Last week, G4S wrote to the BBC to try to stop broadcast of the footage, arguing filming was unauthorised and illegal.
However, Paul Cook of G4S said he was "shocked and appalled" and was supporting a police investigation.
An Ofsted inspection report in September 2014 into Medway rated it as "good with some outstanding features".
Inspectors said the centre was "orderly" and "calm" and young people were said to feel safe.
The centre holds 56 children, mainly boys, aged 12 to 17. It is not allowed to take any more while the investigation takes place.
Among the allegations uncovered by Panorama and now subject to investigation are that Medway staff:
- Slapped a teenager several times in the head
- Pressed heavily on the necks of young people
- Used restraint techniques unnecessarily - and that included squeezing a teenager's windpipe so he had problems breathing
- Used foul language to frighten and intimidate - and boasted of mistreating young people, including using a fork to stab one on the leg and making another cry uncontrollably
- Tried to conceal their behaviour by ensuring they were beneath CCTV cameras or in areas not covered by them
BBC News understands that Ofsted has decided not to publish an inspection report about another STC run by G4S - Oakhill in Buckinghamshire.
The inspection report was due to be released at 10:00 GMT, but a late decision was made not to do so.
Sources said the Ofsted inspection into Oakhill graded it as "good".
The Panorama programme Teenage Prison Abuse Exposed will be broadcast on Monday, 11 January on BBC One at 20:30 GMT.