It would be interesting to try...but the thing about teaching history is so much of the later events are derived from decisions made in past events.

Say you start with Obama and go backwards strictly. What do you talk about without discussing the origin of the presidential powers or purpose in government without talking about the Constitution? It was written over 200 years before, but because you are going backwards you can't talk about it or build on it without inherently negating the purpose of going backwards.

What you could do is start a lesson with a mention of a recent example of a topic you want to cover, ask the class to discuss it in some way, and then explain the origin of topic of the lesson to explain the modern example.

I'm assuming this is a sort of meta question where answers don't really need to be sourced, but if so I apologize and feel free to delete my comment.

I personally don't think it would be a very effective way of teaching a subject, but it would really depend upon what age/level of education in the group. When I've talked to non-history/education people I've always said that teaching history is about understanding the people, places, and events that have shaped and molded the world we live in today. One of the major differences between my secondary education and college education is that high school is more about learning the dates and names, but university education is about understanding why things happened and what immediate and longterm affects they had. In this sense, I just don't believe it would be an effective teaching strategy to teach backwards, especially when dealing with the build up and fallout of major events.

Removed for proposal for speculation, whatif, and violating 20 year rule.