The educational movement is controversial with some trained in the traditional manner, who are skeptical about these programs and their potential to change the tradition. The changes, especially standardization of publishing, are slowly impacting mariachi in Mexico. One difficulty of arranging mariachi pieces is that the "son jaliscense" that mariachi is based on alternates between and time. Much of the published mariachi music is meant for people already familiar with the music to serve as guides, not for novices. On the other hand, many schools have problems recruiting mariachi instructors as many of these do not have required teaching credentials. For this reason, schools often hire trained musicians from outside the mariachi tradition. Many traditional mariachis are concerned that standardization will lead to the genre becoming rule-bound and so restrict improvisation.