Constructivism is a theory of learning that suggests humans construct knowledge and meaning from their experiences. Key theorists like Piaget and Dewey influenced the development of constructivism and progressive education. Constructivist teaching approaches encourage students to take an active role in building understanding from their prior knowledge and experiences through techniques like group work and reflection. Teachers act as guides to challenge students to expand their knowledge. The 5E model provides a framework for constructivist lesson planning, including engaging students, allowing exploration, explaining concepts, extending understanding, and evaluating learning.