Jean Piaget became a veritable institution unto himself in education and psychology, largely as the result of his developmental-stage theory advanced over the second quarter of the twentieth century. Not until Piaget was 73 did he make mention of John Dewey's work at Dewey's laboratory school, founded in 1894 at the University of Chicago. But here he made no mention of Dewey's findings on thinking as a maturational growth process marked by distinctive sequential stages, as explicated by Dewey (1899, 1902, 1910, 1933).This article examines the powerful and unmistakable isomorphism between Piaget's and Dewey's stage theory and the mystery of why Piaget never gave recognition to Dewey's seminal work.