Over all, I am generally a fan of Scholastic’s True Book series, but this one didn’t seem to do as good a job as the others of really getting concrete and clear in its explanations of complex scientific concepts.  Perhaps it was a function of how much material they were trying to cover within the same number of pages, but the information seemed to skim a bit more across the surface level.  It’s not bad, but I think it would have been stronger if it had gone more in depth, maybe having a different volume for each type of simple machine.