Certification of teachers by means other than traditional four-year college and university education degree programs. Candidates for alternative certification hold a degree in the subject matter they will teach and meet abbreviated pedagogical coursework requirements, often during the first two years of teaching.
A predicted teacher shortage has led to experimental methods for certifying teachers in order to guarantee qualified teachers in every classroom.
Advocates argue that the increasing need for qualified teachers demands creative solutions and that alternative certification guarantees that teachers have extensive knowledge of the subject they teach. Opponents argue that abbreviated teacher education fails to develop adequate pedagogical skills and leaves teachers unprepared for the classroom.
For further explanation:
National Center for Education Information has a section that that explores Alternative Routes to Teacher Certification and Overview.