Crackers, lemon juice, and ziplock bags along with a little help from Sid the Science Kid (PBS) and you have a full out digestion experiment.
Lesson plan with visuals, materials list, experiments and lesson guide for your digestive system unit. This grade 4 lesson could be modified to use in other grade levels. From the University of North Carolina school of Education.
KidsHealth.org has a great teachers' guide for grades K-2 and grades 3-5 that you may want to use after sharing the section about the digestive system from their site. Here's a link to visit that site on digestion with your class. They also have a great video you might want to share on this same topic.
Teacher submitted activities about the digestive system can be found at proteacher.org. Try these in your classroom.
The University of Missouri has a printable set of cards that you might want to use with your students to map out the digestive process. Includes a lesson plan, diagram to label, short quiz, and a crossword puzzle.
Make a great model of the entire digestive system - very hands on. From coreknowledge.org.
Brainpop has a short video about the digestive system. They also include lesson ideas and questions that you may want to use to foster discussions in your classroom.
Want a slide presentation about the four different types of digestive systems? Here is one for you - includes a short quiz.
Videos, labeling worksheets, quizzes and more to help you teach about the digestive system. NEOK12.
Penfield High School in New York has a 'downloadable diagram of the digestive system for labeling and discussion. It is designed for high school, but very usable at any grade.
Teachers, this one is just for you. Brush up on your understanding of digestion with illustrations and great text so you will be ready when those difficult digestion questions arise. From Estrella Mountain Community College.