WA schools have lost more than $2.8 million in unpaid debts owed by parents or businesses in the past two years.
Figures from the Education Department have revealed it wrote off more than $1.33 million owed to schools in the past financial year and $1.47 million for the previous year.
The department said the unpaid bills were owed mainly by parents of current or former students for compulsory subject charges, residential boarding fees and overseas students' fees.
A small amount was owed by businesses that used school facilities, such as sporting organisations, dog training or yoga groups.
Deputy director-general for finance John Leaf said compulsory charges applied only to optional school activities.
These included courses that used high-cost materials, excursions such as music tours or tuition not provided by school staff, such as ballroom dancing or martial arts.
"When students choose courses or activities that carry a compulsory fee or charge, parents are made fully aware of the costs involved and schools are entitled to ask for 50 per cent of the charge to be paid up-front," he said.
"The department will only agree to write off a debt if the school can demonstrate it has taken all practical steps to recover the money.
"This might include sending monthly accounts for outstanding costs, reminder phone calls, meetings and, in some cases, asking a debt collection agency to intervene."
Mr Leaf said principals also took into account the person's capacity to pay, given that financial circumstances sometimes changed after a child enrolled in a course.