Enhancing the Curriculum
One of the biggest advantages to field trips is that they allow students to have a real-world experience. This experience should clearly illustrate and enhance information taught by the curriculum. For example, a textbook lesson on the life cycle of a salmon can be enhanced by a trip to a local salmon hatchery, where the students can clearly see the salmon in its many life stages.
New Learning Environment
Field trips also allow the students to learn outside of the classroom. This is slightly different from the first advantage. While the first advantage of field trips is to supplement the curriculum, the second advantage is that field trips offer the opportunity to teach the students something new. A field trip to a local flight museum that features space-flight simulators is going to teach students a lot about rockets that cannot be nearly as effectively taught in a classroom.
A final advantage of field trips is that they are a way to bring the students closer together. Many field trips combine educational content with team-building activities, such as working together to clean a stream that has been polluted. To encourage this team spirit it is often a good idea to go on a field trip early in the school year to help create a bond between the students.
A disadvantage of field trips is that they take an incredible amount of planning. You must figure out transportation issues, chaperons (including background checks), food and alternate plans in the event of inclement weather (if the trip is to a location outdoors). You must make sure that every child has a signed permission form, that you have obtained emergency contact and information available on each student (including allergies), and that all fees have been paid in advance.
Field trips bring up a wide array of legal issues, most regarding liability. If a student gets injured on a nature hike, is the school liable for medical fees? What about the park or the forest ranger leading the hike? Parents may be nervous about the safety of their children. Other liabilities include exposure issues. For example, even a "children's" theatre performance may contain themes or scenes that some parents might object to.