After a decade and a half in the classroom, my best advice for students: ask questions.
Here is a little secret, teachers love engaged students. Many of us went into teaching to work with curious young people, to help them discover more about the world and themselves. Nothing spoils that quite like a group of distracted students, unless it is a group of zoned out zombie students. Just one student who is listening, thinking, and wanting to understand can make a teacher's whole day. With just a little effort, your child could be that student. A simple, "Why does it work like that?" Is all it takes.
Students should also ask questions to clear up confusion. Between the teacher's lesson, directions for assignments, and classroom management, there are a lot of instructions in an hour of class. No student can remember them all. A student should ask right away if he or she does not understand something, because if one student is confused, there are probably others in the room that have the same question. When I was teaching, I had students who would only ask questions after getting the wrong answer on an exam or scoring poorly on a project. By then, it was too late to help. If they had sent an email or stayed after class for 5 minutes, I could have cleared everything up.
Lastly, students should ask questions to show initiative. Teachers create assignments and project for the whole group, but not every student learns the same way. If a student has a clever idea, it never hurts to ask. If the student enjoys making movies, he could ask if he could make a documentary instead of writing an essay. Why not? The teacher may still want him to work on his writing skills, but it shows the teacher that the student is thinking ahead, and perhaps the teacher may create a film making project later in the year. I remember being in a college philosophy class that had one of my last final exams of the year. I asked the professor if I could skip the final and instead write a paper that showed that all of the major concepts that would be covered in the exam could be found in Shakespeare’s Hamlet. The teacher loved the idea, I showed that I understood the concepts, and I got to fly home a day early.
Of course, the delivery of the question matters. The middle of class is fine if the student is confused by the lesson being taught at that moment, but most other questions are best before or after class or by email.