DES MOINES, Iowa (AP) -- A shortage of state-certified sign language interpreters has left some deaf students without the help they need in school.

The Des Moines Register reports that a 2005 law that went into full effect this summer requires sign-language interpreters to obtain a license before working professionally in Iowa.

Critics of the law say the licensing tests are too tough and check different styles of sign language that some interpreters rarely use.

Backers of the law say it's necessary to ensure adequate services for Iowa's hearing-impaired residents.

The Iowa Education Department says at least five districts have unfilled sign-language interpreter positions.