Across the country, districts and schools continue to struggle to meet the growing demand for qualified teachers. Since 2012, when Recession-era layoffs ended, the teacher workforce has grown by about 400,000, as districts have sought to reclaim the positions they had previously cut and replace teachers who have left. But even with intensive recruiting both in and outside of the country, more than 100,000 classrooms are being staffed this year by instructors who are unqualified for their jobs.