This spring, the classrooms of Concord Elementary School in Portland, Ore., buzzed with the ordinary sounds of a grade school: student voices, feet landing on soft carpets, and rustling papers.

But Elizabeth Mueller’s classroom was something altogether different. Mueller’s crisp voice—carried by microphone and a small speaker stationed atop the chalkboard—dominated the room, finding its way even to the most reluctant ear.

For Mueller, a veteran elementary school teacher accustomed to competing with the knock and rattle of an ancient heating system, the microphone has become as elemental as chalk and paper. The fourth-grade teacher no longer strains her voice to get students’ attention. She also knows her hearing-impaired students aren’t struggling to hear her.

Across the country, hundreds of elementary schools have installed microphone and speaker systems in classrooms, libraries, cafeterias, and gymnasiums.

The microphones make it easier for young students to hear their teachers over background noises common in grade-school classrooms.

In the past three years, elementary school classrooms in Oregon’s Gresham-Barlow, Portland, Reynolds, Beaverton, and North Clackamas districts, where Concord is, have been wired for sound at an estimated cost of $1,000 per room.

The result, teachers and principals say, is a dramatic difference in students’ listening and speaking skills.

Students sitting in the last row of the classroom hear as well as those in the front. And because many classrooms are equipped with a second microphone for students to use when speaking, teachers say their students are clamoring to speak out.

“Even if you are timid and shy, everybody hears you and can understand you,” said Lori Prouty, whose son, Spencer, is in Mueller’s class. “It makes a huge difference in the attention span of the kids.”

Audiologists and speech experts say classroom sound systems are growing in popularity nationwide in response to research that shows poor classroom acoustics hinder listening and learning.

An Ohio State University study conducted last year by speech and hearing experts found poor acoustics in 30 out of 32 grade school classrooms in central Ohio.

Voices bounced off hard classroom floors, drowning out words and interfering with students’ ability to listen, researchers found.

The hiss and whir of heating and cooling systems were among the biggest sources of noise.

For children, being able to hear clearly is crucial to developing language, audiologists said.

Poor acoustics compound problems for the hearing impaired; up to one-third of students in primary grades experience some temporary hearing loss due to infections or wax buildup in their ears on any given day.

“Young kids, whether they are hearing-impaired or not, have more trouble in noisy environments because they are still learning their language,” said Lawrence Feth, a professor of speech and hearing science at Ohio State and one of the researchers who participated in the classroom acoustics study.

“They need even quieter backgrounds or stronger speech signals in order to get the same level of information that adults have,” he said.

Teachers have long tried to compensate for poor acoustics by laying pieces of carpet on tile floors or sticking tennis balls on the feet of metal chairs to keep them from scraping.

Some schools hang sound-absorbing paneling on walls to dull noise.

Microphones are just the latest way educators are trying to improve sound quality in the classroom. And there is evidence to show that it works.

A 1993-’95 study done in Florida found children in amplified classrooms paid attention longer, completed their assignments in reading and math, and generally maintained an academic edge over their peers in nonamplified rooms, said Gail G. Rosenberg, an audiologist with the Sarasota schools in Florida and one of the study’s leaders.

Rosenberg works with students with hearing impairment and evaluates classroom amplification systems in Sarasota schools.

The study involved 94 classrooms in 33 schools and is the most comprehensive look to date at the effectiveness of microphones in the classroom, it was reported.

In addition to improved performance among students, the study found that microphones protected teachers’ voices, Rosenberg said.

“Teachers are less stressed, because their voices aren’t damaged or strained the way you are when you have to project over everyone,” agreed Thelma Rueppell, principal at Bethany Elementary in Beaverton, Ore., where classrooms also are amplified.