Union remains cautious despite Lord Chancellor's promise of greater legal safeguards for teachers.
Teachers have welcomed new laws designed to protect schools from being unfairly sued over accidents on school trips.
Lord Falconer, the Lord Chancellor, said fear of legal action was restricting activities and anyone who acted reasonably should be protected against unfounded claims. He cited pupils wearing goggles when playing conkers as an example of the "culture of fear".
The Compensation Bill, published last week, would allow courts to consider the wider social value of activities when considering a negligence claim.
Chris Keates, general secretary of the NASUWT, said the Bill was a step in the right direction but that the teaching union was not changing its advice to teachers to think about the risks they face before taking part in school trips.
She said the union had never advised teachers simply to refuse to take part in school trips.
Geoff Lucas, general secretary of the Headmasters' and Headmistresses' Conference, said there was a feeling among schools that red tape and legal risks had made them too cautious about trips.
"This has to be a positive move," he said. "While we are not aware of a huge drawing back from trips, schools have become concerned to ensure that proper risk assessments are in place, and that they have followed all the procedures."
A spokeswoman for the National Union of Teachers said the new laws would create a better atmosphere for teachers organising trips. She said: "High-profile cases in the media have given teachers an exaggerated sense of the risks they face."
Two years ago Paul Ellis, a geography teacher at Fleetwood high, Lancashire, was jailed for a year for manslaughter after the death of a 10 year-old boy during a school trip to the Lake District.
The Compensation Bill also aims to clamp down on unscrupulous claims-management firms by introducing a code of practice.
The Government launched a "manifesto" for school trips that aims to give every child the chance of at least one residential activity. It also plans to support schools and local authorities in safety planning for school trips and reducing bureaucracy.
Teachers will be given guidance and resources, and be urged to join up with other schools and providers of outdoor activities such as the National Trust to get the best from school trips.
A spokeswoman for the Association Teachers and Lecturers said: "Off-site activities help develop social skills, knowledge of the world, and are a fun part of learning for young people. They should be encouraged and supported."
The manifesto was welcomed by the National Trust. Tony Burton, director of policy and strategy, said: "Teachers need to feel confident in planning and supervising visits and know they are working with reputable providers."