I taught adolescents for about ten years, first as a Peace Corps volunteer in Liberia, and then as a public school teacher in eastern Oregon. Along the way, I took many teaching methods classes.
There's been a substantial amount of research into the ways people -- particularly children -- learn and a commensurate number of recommendations for the best ways to teach. Nothing very earth shattering has been discovered, and good teachers have pretty much always done the same things.
Successful teaching involves the incorporation of a few key principles into one's lessons. Though not an exhaustive list, a successful teacher is likely to:
1. Respect their students, and require that their students be respectful of each other and the teacher.
2. Plan lessons that move from the known to the unknown.
3. Check often, as continually as possible, for understanding.
4. Explain things in more than one way more than one time.
5. Recognize that people learn by doing and give their students much to do.
6. Recognize that the people doing the talking are the ones learning: avoid lecturing.
The reason I mention any of this is because I don't think that number 2 above is understood or used appropriately in much science education, at least not when it comes to anatomy and physiology.
One of the guiding principles of good teaching related to the basic notion of moving from the known to the unknown is to move from the simple to the complex. This is the reason that so many biology curricula have students dissect grasshoppers, crayfish, earthworms, and starfish. Of course, there is nothing simple about the biology of any of these animals.
How should we teach anatomy and physiology? Basic pedagogy suggests that students ought first think about and investigate something they know and then learn about other things that their prior understanding can build on.
The first thing most students ought to explore is their own hand. They can see and feel the movement of tendons and bones and can see blood vessels through the skin. This would lead to an investigation of the arms, the legs, and the entire human body. They could palpate some of their own organs, and use that firsthand experience to make sense of drawings and models of the human anatomy.
Their own body is a structure that students know intimately. This is a reasonable and likely fruitful place to begin any sequence of lessons on anatomy and physiology. They ought to have a strong grasp of their own biology before investigating the biology of very dissimilar organisms.
The study of the anatomy and physiology of animals like grasshoppers, crayfish, earthworms, and starfish -- or frogs, pupfish, or whatever animal is being dissected -- more appropriately belongs in a comparative physiology class for students with a good understanding of human anatomy and physiology.
Unfortunately, elementary teachers wishing to provide hands-on experiences for their students (number 5, above) and junior and senior high school biology teachers commonly believe that it is easier to understand the anatomy and physiology of "simpler" "less complex" animals "lower" on the "evolutionary scale" and that by cutting up these animals, students will gain important knowledge. These teachers mean well, but their embrace of such practices suggests that they don't understand the implications of evolution, they don't care about animals, and they don't understand how people learn.