I recently finished reading this book aloud to R*. Before starting it, all I knew was that it was a classic children's book about a black horse. Well, that's true but I was impressed to find out that it's really a morality story. Many of the morale lessons are directed at animal welfare but there's plenty of dialogue lecturing about social morality and how to treat our fellow man. This is constantly illustrated through the stories of the owners of Black Beauty, especially that of Jerry Barker.
What makes it particularly interesting is that it was written in 1877 and provides some insight into what life must have been like back then. Poor horses! The language can be a bit arcane at times but it's quite approachable for an eight year old. It's a classic for very good reasons. Since the copyright has expired, you can get it online.