@book{111356,
	author = {Porrata, Oscar Emilio},
	title = {Retardation in the elementary urban schools of Puerto Rico},
	publisher = {The University},
	year = {1939.},
	series = {University of Puerto Rico bulletin},
	address = {Rio Piedras, P.R.},
	note = {Thesis (M.A.)--University of Chicago, 1934.}
}