After you've given students a basic foundation in defining and understanding endangered species, devote each subsequent lesson to a specifically endangered species. For example, during one class you could talk about wolves and the following day you could talk about sea otters, and the next day you could talk about the jaguar, and then the Florida black bear and so forth. Devoting specific lessons to each animal not only gives students comprehensive knowledge, but a better overall perspective.
One of the strongest ways to get kids to understand and retain information about endangered species is to require that they teach the lesson. Do this by assigning each student an individual endangered species to research and create a short presentation about. Students in the class must listen to their fellows students' presentations and ask informed questions. This will cause students to have a greater retention of knowledge than if they were just passively listening.
One of the issues with teaching elementary school lessons on endangered species is that kids might easily feel helpless, as though they're too young to do anything about it. Devote lessons to things they can do to help these animals and their habitats. For example, you could have a class trip to an animal or nature reserve to find out about threatened animals and what kids can do to help protect them. Kids might even be able to volunteer and help the rangers. Alternatively, you can take kids on a field trip to help restore native animal habitats by removing rubbish and replanting bushes and shrubs to encourage animals to return.
Asks students to turn the foundational knowledge that you've provided them with into a creative project. For example, tell the class that you're all part of an art agency and that together you'll be making a book on endangered species. From this point on you can assign children to specific species to research and to draw, so that when finished, the class can assemble everyone's work into one large book. Alternatively, draw a "Web of Life" for the kids, which shows how the species inter-relate and impact one another and then ask students to draw their own versions of the web of life, focusing on a particular branch of the animal kingdom.