Microphones for teachers pump up the volume

Hanging from the necks of elementary school teachers, little black devices, the shape and size of small cellphones, have begun to appear in hundreds of classrooms in the Washington, D.C., area. They are infrared microphones, designed to raise the volume and clarity of teachers' voices above the distracting buzz of competing noises—the hum of fluorescent lights, the rattle of air conditioning, the whispers of children and the reverberations of those sounds bouncing off walls and floors. The Prince George's County (Md.) district is spending up to $1 million a year to install the systems in every classroom.

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