Many schools struggle to meet their legal requirements for daily collective worship in England (or regular acts of Religious Observance in Scotland). Some schools have no Christian staff, or nor anyone willing to take this responsibility. This is where church groups can help.
There are many good Christian resources available for collective worship that a church could recommend to a school. Church members could offer to purchase resources for the school to use. (For a good range of resources for Christian collective worship, check out the bookshop or resources sections of www.stapleford-centre.org. Barnabas also has a range of collective worship and other resources available at www.barnabasinschools.org.uk.)
The church and school together could host training events for teachers and children's workers, such as puppet workshops or creative arts events, to make sure that collective worship is relevant and intelligible to pupils.
You may decide to invite a church leader to visit your school to lead collective worship. Bear in mind that this may not be his or her gifting. But it is possible that there are other church members who are more gifted for working with children and they would probably be the better person to come into the school. Discuss that with the church leader. Some churches or groups of churches have created 'school assembly teams' who are skilled at communicating the Christian message to children, in leading collective worship and which can serve a number of schools in this way.
Talk to other local headteachers to see if such a team exists in your area. Even one gifted individual church member can make a huge difference to a school in this way. Leading collective worship usually forms a big part of the work done by Christian schools workers, so if there is such a team in your locality, contact them and invite them in to meet them and discuss how they can help you.
If church members do come into your school to support you by leading collective worship, then prepare them with advice about the familiar pattern for the pupils and the songs they know etc. Everyone, the church team and the pupils, will benefit if you can give some constructive feedback afterwards about what went well and the sorts of things that the pupils engage with and enjoy.