Virginia Escobar-Cheng teaches a science class at a high school in Homestead, Florida, in March.

Schools throughout the country are grappling with teacher shortage, data show

Updated 1745 GMT (0145 HKT) August 21, 2017

(CNN)Lynn Sorrells started teaching 26 years ago because she loved seeing the light-bulb moment when a kid grasped a new concept.

She still does. But as principal of a high school in Dorchester County, Maryland, she is struggling to find an algebra and geometry teacher just weeks before her school year is set to begin.
As students head back to school, Sorrells' district is one of hundreds across the country grappling with a growing teacher shortage -- especially in key areas such as math and special ed.
"Currently, there are not enough qualified teachers applying for teaching jobs to meet the demand in all locations and fields," said the Learning Policy Institute, a national education think tank, in a research brief in September.
Some schools, such as in New York City, are being forced to increase class sizes, which some studies show can reduce how much a student learns.
The institute estimated last year that if trends continue, there could be a nationwide shortfall of 112,000 teachers by 2018.

What subjects are most affected?

Public schools in 48 states and the District of Columbia report teacher shortages in math for the 2017-18 school year, according to the US Department of Education. Forty-six states report shortages in special education, 43 in science and 41 in foreign languages.
Statistics on shortages may be based on the percentage of unfilled teaching jobs, the number of emergency credentials given to those without traditional teaching certificates and the number of teachers hired after the school year starts, says Dan Goldhaber, director of the University of Washington's Center for Education Data and Research.
It's always been harder to fill teacher jobs in math, science and special education positions, Sorrells said. But the past five years have been worse than usual.
Increasingly, she said, teachers in areas like math and science are leaving for higher-paying private sector jobs after a few years.
As a result, many teachers who remain are being asked to do more. Some states, like California, are seeing classes with up to 35 students, says Linda Darling-Hammond, director of the Learning Policy Institute.
And some schools are making do without certain subjects.

Is there help on the way?

Probably not soon. The supply of aspiring teachers has been dwindling.
Nationwide, teacher education enrollments dropped 35% between 2009 and 2014, the most recent year for which data are available, according to the Learning Policy Institute.
A survey at UCLA found that freshmen's interest in teaching as a career has steadily declined over the past decade.
And in Colorado, for example, the number of people becoming teachers and administrators fell more than 24% from the start of the 2010-11 school year to the end of the 2015-16 school year, according to the Department of Higher Education.

So what's causing this?

Goldhaber, who studies educational trends at the University of Washington, sees two main reasons.
Math and science teachers aren't paid enough. Salaries for US secondary school teachers have largely remained the same over the past two decades, according to the National Center for Education Statistics.
And students in the STEM fields (science, technology, engineering and math) can make more in other professions than they would teaching.