As for the teaching of history, Ms. Ravitch argues, the sort of censorship being practiced today by textbook publishers can result in all manner of distortions and simplifications. For instance, to insist that depictions of women as nurses, elementary-school teachers, clerks, secretaries, tellers and librarians perpetuate demeaning stereotypes is to minimize ''the barriers that women faced,'' and to pretend ''that the gender equality of the late 20th and early 21st centuries was a customary condition in the past.''