The Lorax" has a number of very obvious learning points and as such is a book which has a lot of potential for use in schools. However, it can be difficult and time consuming figuring out how exactly to use a book like this in an educational fashion. Luckily, the internet brings us a number of lesson plans that use the situations in The Lorax book and extrapolate upon them.
Free Green Lesson Plans; Dr Seuss, The Lorax
The above link will take you to a simple and logical lesson plan, developing ideas around the environmental aspect of the story. It starts with Lorax themes and then moves on to wider environmental issues.
A small collection of other lesson plans based upon The Lorax can be found here - Lorax Lesson Plans.