From its foundation the School has been linked with the teachings of the Church of England. However, girls of all denominations and faiths are welcomed and encouraged to make a positive contribution to the religious life of the community. The Parish Church of  the Holy Trinity is situated almost within the grounds and provides the perfect setting for services, concerts and recitals. The Chapel Choir is an integral part of Casterton's strong musical tradition.

The resident Anglican Chaplain is always available to offer help and guidance, and to prepare the girls for Confirmation. The School worships together on Sunday mornings. The occasional Choral Evensong or House Evensong (devised and conducted by the girls themselves) adds variety to the regular programme. Worship is presented in a lively and stimulating way with a good deal of informality and interaction. Arrangements are made for Roman Catholic pupils to attend Mass on Sundays.