tries to explain seismic waves to this eighth grade class. >> all right, so we know it's 8:30 because this is our 8:30 block. >> reporter: two years ago,the r was spending his days month floors as a school custodian. >> this is definitely a change. >> reporter: do you feel this is a calling? >> definitely, definitely it's a calling. like i said, it was something i wanted to do just didn't know how it was going to happen. >> reporter: facing a growing teach shortage, the clarksville-montgomery county school district launched an innovative teacher residency program in 2018, recently registered as the first of its kind in the country. shawna is the district's chief academic officer. if you didn't have this program in place right now, how bad would the teacher shortage be? >> we would have had about 150 teachers short. >> reporter: the program squeezes a four-year degree into three. night school is free, and they coteach during the day with a mentor, earning up to $27,000 a year. when they graduate, their salary almost doubles opinion how will