Throwing the teacher a surprise party shows her that she is appreciated. The teacher will likely not expect the party and when it occurs she will be pleasantly surprised. At the party, organizers can serve food and arrange for a slideshow or speeches. Organizers may choose to invite former students as well.
Taking the teacher out to an upscale restaurant for dinner can help show appreciation and also give the teachers and students a chance to get to know each other outside of the classroom. This type of gift works well with adult students. Find out what food or restaurant is the teacher's favorite before making reservations.
Gifts are an easy way to show appreciation. The best gifts are those that come from the heart. A book for the teacher from her favorite author or genre is an inexpensive gift she will appreciate. For congregations that really want to show their appreciation to the hard working teacher, arranging a vacation or enrolling her in a workshop can be exactly the break she needs.
Perhaps the best gift for a Christian teacher is to know that his students have learned the lessons of the class. If the students each prepare a report (written or oral) of how the class and teacher have helped them in their lives, the teacher will know that the work he is doing is making a difference.