A Teacher Shortage is a situation where a nation's education system is too small to keep up with the demands of the population, upsetting Parents and causing a drop in Literacy from the number of kids going without educations.
The main cause of teacher shortages are poorly funded State Schools and a high rate of Immigration. Raising the level of school funding is the easiest and best way of fixing the situation, but reducing immigration will also help the system by reducing the number of students.