Too many further education colleges and skills providers are leaving students at risk of radicalisation and extremism, watchdogs have warned.
A "worrying" number of institutions are struggling to put in place a new government requirement to prevent people being drawn into terrorism, Ofsted said.
In some cases, they had not implemented any aspect of the duty - a key plank of the Government's efforts to counter extremism - while others were said to have adopted a "tick-box" approach.
Inspectors also raised concerns about "inadequate" vetting and monitoring of external speakers, and arrangements for guarding against online radicalisation.
Reports have emerged of young people leaving their studies to become involved in terrorism either in Britain or abroad.
From September, further education and skills providers were placed under a duty to have "due regard" to the need to prevent individuals being drawn into terrorism.
This includes preventing extremists from seeking to radicalise learners and supporting those perceived to be at risk of extremist influence.
Ofsted carried out survey visits to 37 further education and skills providers, as well as 46 full inspections or monitoring visits between November 2015 and May 2016.
Its report found:
::Thirteen providers had been slow in putting the duty into practice;
::Two out of eight independent learning providers visited had not implemented any aspect of the Prevent duty;
::Vetting and monitoring of external speakers were inadequate in around a quarter of the providers, with six having no arrangements to check their suitability.
::Nearly half of the providers lacked sufficient online safeguards, with learners in some cases bypassing security settings to access websites selling firearms or promoting terrorist ideology;
::In one instance, an individual accessed a terrorist propaganda video showing a beheading.
::Twenty-two of the 37 providers visited had implemented the Prevent duty well, with general further education and sixth form colleges the most successful;
Ofsted's deputy director for further education and skills Paul Joyce said:"It is reassuring that over half of the providers visited for this survey were found to be making good progress in implementing the Prevent duty, and are ultimately keeping their learners and local communities safe.
"Leaders in the general further education and sixth form colleges we visited should be commended for the quick progress they have made in implementing this new responsibility.
"However, it is concerning that in some colleges and providers the progress made in implementing the duty has been slow. It is worrying that inspectors saw examples of poor practice that I've no doubt would shock parents and learners alike.
"I am calling on providers, local authorities and the Government to take on board Ofsted's recommendations. We need to work together to ensure that we keep learners safe and protect them from all forms of extremism."
Ofsted called on the Government to ensure Prevent duty advice is offered consistently, while it said providers should ensure learners have "a good understanding of British values and the risks and threats of radicalisation and extremism".
Skills Minister Nick Boles said: "Further education providers have a duty to educate but also protect their learners.
"This report provides useful insight into the initial progress made by the sector in the weeks and months after the Prevent duty was introduced last year.
"While the majority of providers have worked hard to implement the safeguards effectively, we recognise there is still further work to do in making the Government-funded guidance and training as consistent as possible."