A three-year study of primary school classrooms has shown that many have problems with acoustics - with pupils struggling to hear and teachers having to shout to make themselves heard.

Researchers from Heriot-Watt University in Edinburgh have found that children sitting in parts of classrooms with particularly bad acoustics - "dead spots" - can miss out on whole lessons.

Researchers found that a majority of primary schools had problems with sound

The study, which examined 70 primary schools in England, Scotland and Northern Ireland, also found a correlation between poor acoustics and higher rates of sickness among staff - with increases in sore throats and stress.

The researchers have concluded that schools need to consider acoustics when building new classrooms and when renovating existing buildings.

Classrooms without carpets and high ceilings can create particular sound problems - and the researchers suggest that audibility can be greatly improved by introducing lower ceilings.

In an attempt to measure the difference, suspended ceilings were installed in Balgreen primary school in Edinburgh, with the staff welcoming the improvements in audibility.

"Staff working in the treated classrooms say there's an enormous difference," said headteacher Kathleen Douglas.

"Not only do they not have to shout to be heard, but there's a generally calmer, quieter and more relaxed atmosphere in the classroom, which has positive effects on behaviour and reflects the ethos of the school."

The extent of the problem surprised researchers, who found that poor acoustics were affecting a majority rather than a minority of schools.

"When we started our research we thought we might find a few classrooms where poor acoustics caused some problems," said Sharon Airey, a research associate at Heriot-Watt.