How can I teach a grown dog to sit?

Have you ever thought about using a treat to do it? First, get down on the pet's level if possible by crouching down, and then take the treat and guide it downwards and say sit gently but firmly to the pet. That is how we learned to do it in class.

The treat helps to guide the animal to do the actual task. You can use a favorite toy to do it as well. I hope this helps!