School inspections are being suspended by the government during the coronavirus pandemic following pressure from teachers.
It came after the government faced mounting calls from school leaders and teachers to remove the checks.
The National Education Union said inspections were “unacceptable” as all schools in England had already been affected by the coronavirus outbreak.
Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), also urged for inspections to be suspended immediately amid a time of “national emergency”.
In a video posted on Twitter on Tuesday, Mr Williamson acknowledged that staff shortages are presenting teachers and headteachers with “great challenges”.
He said: “I also want to remove unnecessary burdens to help schools to cope. Given the pressures on our school leaders and their staff, it is only right that Ofsted temporarily suspends its routine inspection timetable.
“This will help schools to focus on their core functions at an already very difficult time.”
Amanda Spielman, Ofsted’s chief inspector, said: “It’s clearly the right thing to do when teachers and social workers are under pressure as a result of the coronavirus outbreak.
“We all need to support them in their work.”
Urgent inspections where safeguarding concerns have been raised will still be carried out, Ofsted said.
She added: “We will monitor what’s happening across education and social care and we will reserve the right to inspect where we believe the safety of children could be at risk, or we have other serious concerns.”
Paul Whiteman, general secretary of school leaders’ union NAHT, said: “We now expect the same to be said of all performance tables and other accountability measures.
“The government has placed a significant responsibility on schools to stay open in order to keep other areas of society functioning, at least in the short term.
“It would be entirely wrong to hold schools to account in the normal way when the situation we are facing is far from normal.
“The government must move quickly now to provide clarity for the dedicated public servants working in education about what the state expects them to do.”
Additional reporting by PA