The layoffs of teachers nationwide during the recession years of 2008-2012 has now led to a shortage during an improving economy where many are training for other fields with better pay. School districts are now struggling to find teachers in the math, science, and special education fields, as well as those who are bilingual due to an increase in students who need to learn English. States like California, which had lost 82,000 jobs during the recession, will have to fill 21,000 vacancies this year. Some districts are offering on-the-job training to those who have not yet completed their teaching credentials.
See "Teacher Shortages Spur a Nationwide Hiring Scramble (Credentials Optional)", Motoko Rich, August 12, 2015