Wages aren't the only reason teachers are striking

Schools in 39 of 50 states have seen decreases in funding for instructional materials for their students, according to data from the Urban Institute. These conditions have sparked a wave of teacher activism across the country.

Why it matters: Educators have had to pay for supplies themselves to provide new materials for students at times. Teachers' salaries aren't enough to pay for materials, either. In some cases they have to pay for materials for dozens of children.

The big picture: Teachers are having to teach students with materials that are defective, outdated and inefficient because of a lack of funding going to state education budgets — particularly in Republican states.

"We've got to call it what it is ... teachers are begging to be heard and they're begging to have what they need to do their jobs well,"

Behind the numbers: Costs for instruction materials per student have only risen six percent, from about $281 to $265, since the year 2000.