Churches are very diverse groups of people and a rich source of possible people who might contribute to a lesson to enhance the teaching and learning.
Religious education and collective worship (or religious observance in Scotland) are obvious areas of the curriculum where Christians can be involved. But don't just limit their contributions to those areas. Often members of the church congregation will have interests, expertise and knowledge in other areas of the curriculum and they are then able to contribute and help to bring the subject alive.
History is often an area where older members of the congregation can share their life experiences and show pupils relevant artefacts - this will have the pupils enthralled.
Church members may originate from, or have travelled to, all parts of the globe. They, together with visiting missionary links to the church, can also enrich the pupils' learning if invited to come to talk about where they work or were born and live. Your school may like to make a global link with a Christian missionary as a focus for global citizenship work or to support their charitable projects. For staff and older pupils, this may open up opportunities to visit or to work with a Christian aid or relief agency.
Doctors, nurses, health professionals, engineers and scientists may all have things that you can draw upon for science lessons. Church members may also have expertise that can be of use in art, music, sport and design lessons.
Many topics in your religious education syllabus would be enriched by first-hand encounters with Christians who can explain what they believe or practice, e.g. topics such as 'What do Christians believe', 'Sacred texts', 'What Christians believe and how that informs ethical and moral choices, including forgiveness and issues of good and evil'.
There are many ways Christians can contribute to a religious education lesson. Some schools invite a group of people from a variety of religions to contribute to a 'Face the panel' type of lesson and answer questions about their faith. A variation on this is 'Grill a Christian'. This usually results in pupils asking some very searching questions.