When a student knows the answer than they answer it rather than when they don't know. When a student pays attention then they know the answer. The class participation is a really simple way for a teacher to give marks to students. Rather than giving big, big assignments. Which will take them time to think about the assignments for the kids, mark the assignments, and help the kids improve where they need improvement. And this would not only be bad for the teacher but the students who pay attention in class and know everything because they will not be able to learn new things. Everyone is different, some like learning and some don't. The one's who don't like learning will not be interested in what there learning, but they do the assignment because they want the mark.
I am a "gifted student", and before I had the option of harder classes, I did not participate in class. Why listen to someone tell you information you already know? My time was better spent sneakily reading about things I did not know. Participating actually made me frustrated by the lack of learning. Listening to teachers repeat things gave me headaches and made me dislike school.
I participated very rarely in class but I was a very smart child and a good student. My main reason for avoiding participation was that I was shy and I was bullied, so I tried to avoid attention and situations where people would watch me or criticize what I said or did. This is something that sadly happens fairly often in schools.
Class participation is not at all reflective of a student's intelligence. Students choose to participate or not to participate for many reasons. Many times a student who does not participate is actually quite intelligent. For example, the material may be too easy for them and they are bored and do not participate in class.
Students who are bored, gifted or simply aware of how the system works often do not participate in class, especially if the content is meaningless to them. Like adults, students do not wish to participate in an activity or discussion unless it is important to them. It has no reflection on whether or not they are intelligent.