Leveling reading books for students

I'm a teacher. I'm trying to find a app that can help me find the reading level of a book. I'm having a hard time finding an app for the Android that does this. iPhones have apps like level it, book retriever, book wizard, etc. I did find an app called library leveler but it didn't have very good reviews. does anyone know of any good apps from the Android that can level books?