By Katherine Sellgren
BBC News education and family
Pupils are using new technologies on a regular basis
Pupils given a greater degree of freedom to surf the internet at school are less vulnerable to online dangers in the long-term, inspectors say.
"Managed" online systems were more successful than "locked" ones at safeguarding pupils' safety, they said.
In a report, Ofsted said the area most in need of improvement was online safety training for teaching staff.
The report was published in E-safety Week, which aims to raise awareness of some of the dangers of technologies.
The inspectors' research was commissioned in response to a report by Dr Tanya Btron, which assessed the risks children faced when using the internet and video games.
Ofsted inspectors visited 33 primary and secondary schools, a special school and a pupil referral unit and found e-safety was outstanding in five, good in 16, satisfactory in 13 and inadequate in one.
The five schools judged outstanding for online safety all used managed systems to help pupils become responsible users of technology.
These systems have fewer inaccessible sites than locked down systems and so "require pupils to take responsibility for themselves".
Inspectors said that while the 13 schools using locked down systems kept pupils safe while in school, these systems were less effective in helping them learn how to use technology safely.
The report - the safe use of new technologies - said: "The schools where the provision for e-safety was good or better recognised the potential dangers of new technologies, but tried to equip their pupils to deal with them.
"Where the provision for e-safety was outstanding, the schools had managed rather than locked down systems.
"In the best practice seen, pupils were helped, from a very early age, to assess the risk of accessing sites and therefore gradually to acquire skills which would help them adopt safe practices even when they were not supervised."
The report praised one local authority where schools had adopted a "think before you click" policy, encouraging pupils to ask themselves questions such as "can I be sure people are who they say they are?" and "what information about myself should I not give?"
The inspectors said their main concern was poor levels of staff training in online safety.
"E-safety training was usually weak when the head teacher had not delegated responsibility for it. The training tended to be informal only," the report said.
The best training was planned systematically and included all teaching and support staff, it added.
A new e-safety campaign uses cartoons to teach children
The Ofsted report called on the Department for Children, Schools and Families, Becta (the government's agency for promoting ICT) and the Child Exploitation and Online Protection Centre (Ceop) to do more to help schools improve e-safety.
Chief inspector Christine Gilbert said: "New technologies are central to modern life and provide a powerful support for learning, but they can also present a risk for young people if they are not taught how to use them safely.
"Children and young people do not always have the knowledge, skills and understanding to keep themselves safe and so it is essential that our schools teach them how to stay safe online."
Ceop welcomed the report findings, saying it would ignite future debate.
Chief executive Jim Gamble said children needed to be empowered to use the internet rather than "mollycoddled".
Mr Gamble said, in the real world, adults would not block children from going to the park, but would help them mitigate any risks involved.
"The best way for children to manoeuvre these websites effectively is through experience," he said.
Stephen Crowne, chief executive of Becta, said: "The internet is an incredibly powerful tool for learning, offering a wealth of resources and information but we can't deny there are potential threats out there.
"Schools and parents need to work together to ensure that students use it responsibly and safely -whether in or out of the classroom."
On Tuesday, the UK Council for Child Internet Safety launched a campaign to raise awareness of e-safety among young children.
The campaign uses cartoons to show five to seven-year-olds that people are not always what they seem.