WASHINGTON (AP) -- Nearly all public school teachers report digging into their wallets to pay for school supplies, spending nearly $480 a year, far more than the federal $250 tax deduction available to teachers.

That's according to a study by the National Center of Education Statistics released Tuesday.

The report comes at a time when teachers across the country are walking out of classrooms to protest low pay and demand pay raises. Helping teachers pay for supplies was a key demand during the Arizona teachers' strike.

According to the study, 94 percent of public school teachers say they spent their own money to pay for supplies in the 2014-15 school year without reimbursement. The average amount spent was $479. About 44 percent spent $250 or less, while 36 percent spent $251 to $500.