If someone is docile, he is easily taught or handled. If you suddenly became a trouble-maker in class, your teachers would long for the days when you were sweet and docile.
Docile comes from Latin root for teaching, docere, so someone docile is easy to teach. A docile student is willing to be taught. A docile animal is easy to handle. If you behave well and do what people tell you to do, you're a docile person. Docile might be a word of praise, but it can also be a criticism of someone for being overly submissive. Some synonyms are amenable and compliant.