Ginsburg, H., & Opper, S. (1969). Piaget's theory of intellectual development: An introduction. Prentice Hall.

Ginsburg, Herbert, and Sylvia Opper. Piaget's Theory of Intellectual Development: An Introduction. New Jersey: Prentice Hall, 1969.

Ginsburg, Herbert, and Sylvia Opper. Piaget's Theory of Intellectual Development: An Introduction. Prentice Hall, 1969.