In Oklahoma, 30,000 teachers have left the profession in the past six years. That’s the eye-popping statistic that stands out in the latest Oklahoma Teacher Supply and Demand report, and it represents a loss of an average of 10 percent of the state’s teaching workforce—compared to a national average of 7.7 percent attrition.

It’s been nearly one year since teachers descended on the Capitol en masse, shuttering schools across the state in a quest to secure more funding for education. The report’s findings echo those teachers’ frustrations. Classes are larger, teachers are less experienced, and hiring is a struggle.

A statewide pay increase went into effect this year, giving all teachers a boost of an average of $6,100, and the Legislature seems likely to pass an additional $1,500 raise this legislative session. But that only addresses one slice of the teacher shortage; there are other reasons teachers are leaving the profession or not pursuing it to begin with.

Here are five things to know.

The student population is shrinking in most of the state.

Central Oklahoma, which includes the Oklahoma City area, is the only area with a growing student population—and consequently the highest demand for teachers. Growth in the central region is expected to continue through 2021 before leveling off. Central Oklahoma also has the highest student-teacher ratio (14 to 1), well above the state average. Each of the other regions across the state, including the Tulsa area, is experiencing a decline in the number of students.

Turnover and student-teacher ratio are highest in charter, middle and high schools.

Teachers in charter schools, middle schools and high schools have experienced the sharpest increase in the number of students. These teachers also have the highest turnover rates. The ratio of students to teachers (which is similar to class sizes) has increased 52 percent in charter schools in the past six years, reaching 43 to 1 in 2017-18. Middle and high school teachers in nearly all subjects have seen their student loads increase dramatically, particularly for physical education, computer technology and foreign language classes.

Roughly half of all teachers quit teaching within five years.

Oklahoma’s ability to retain teachers is bad and getting worse. One out of five teachers quits after one year. Paraprofessionals are most likely to stay, with a 91 percent retention rate, and emergency-certified teachers are least likely, with a 73.6 percent retention rate after one year. After five years, just over half of all the teachers remain. A survey of Oklahoma’s “reserve pool,” a group of certified educators who aren’t currently teaching, found that pay matters more to younger teachers; those with experience value having control over instructional decisions, standards and curriculum.

Fewer new teachers studied education in college.

New teachers are more likely to find their way into the classroom through a nontraditional certification path. While teachers with a standard certificate are still the norm (three out of four), less than half of new teachers obtain a standard certificate, which is for teachers with a degree in education. Emergency certificates are the fastest-growing certification category, with 18 percent of all new teachers in 2017-18 taking this path, but they comprise just 2.2 percent of all teachers.

Fewer teachers have advanced degrees.

Teachers today are less likely to have an advanced degree and are less experienced than five years ago. The percent of teachers with a master’s degree decreased by nearly six percentage points from 2012-13 to 2017-18; the average years of experience dropped by one year during that same time, to 12. These trends drive down the state’s average teacher salary, which in turn decreases the supply of teachers, who choose a different occupation or take a job out of state.