Constructivism is a learning theory where students actively construct their own understanding and knowledge through experiences and reflecting on those experiences. There are two main types of constructivism: cognitive, which focuses on individual understanding, and social, which focuses on social interactions. Key theorists who contributed to constructivism include Piaget with his stages of development, Bruner who emphasized active learning, Vygotsky who discussed social learning, and Dewey who advocated for student-centered learning. In a constructivist classroom, students would work collaboratively to solve problems, reflect on their learning, and use inquiry-based methods to build upon their prior knowledge through hands-on experiences.