- 20 Questions - Online game
- Template for Twenty-one Questions: Download a pdf file dichotomous decision tree and make an overhead transparency or project with a data projector.
- Bug-Net: Online Insect identification resource.Use this online key to identify insects.
- USDA Plants database: The United States Department of Agriculture database of plants. Although this does not have a complete dichotomous key, it can be used to explain the classification process.