Constructivism is a learning theory where students actively construct new knowledge based on previous learning and experiences. Key contributors include Piaget, Bruner, Vygotsky, and Dewey. According to constructivism, learning occurs best when students form hypotheses and conclusions through hands-on projects and problem solving. Teachers should understand each student's development level and encourage assessment of learning. Classrooms using constructivism have students apply prior knowledge to hands-on activities, work collaboratively, and use technology like videos, virtual tours, and online games to construct new understandings.