I am afraid you are confused as to what constructivism is. Constructivism is a learning theory. It is NOT a teaching theory or anything that has to do with teaching methods or how bad or good a teacher is. When you are learning something you are "constructing" new knowledge. You make connections with things that you already know (prior knowledge). That can happen in a discussion or in a lecture, it doesn't matter because constructivism is about learning and not teaching.