Constructivism is a learning theory where students learn by actively constructing their own understanding and knowledge through experiences and reflecting on those experiences. Some key principles of constructivism include students learning by doing, motivation being key, and learning taking time as students ponder concepts and develop their own understandings with guidance from teachers. Constructivists like Dewey, Montessori, and Kolb advocated for hands-on, experiential learning where students interact with their environment and answer their own questions. In a constructivist classroom, students work in groups to analyze information and build upon their existing knowledge independently with teachers asking guiding questions rather than providing direct answers.