An objective often allotted to the teaching of threatened languages, rarely if at all transmitted un the family, is, quite simply, to save them. The study of the situation in Basque Country, where the number of young speakers increases appreciably thanks to schooling done in the Basque language, shows that knowledge and use do not necessarily go hand in hand. An outline of the factors inducing this variation is given. The development of an effective linguistic policy must take this factors into account.