Horrified at the waste of carbon - the non-metallic element that makes light bulbs glow - they called for only one light to be on in the early hours, especially in summer months. During the daytime, stickers have been placed under every switch reminding staff and pupils to turn off lights and computers when leaving rooms.
The energy-saving strategy has shown that it's the simple things that make a real difference. Chair of the eco-committee Kieran Eveleigh, aged eight, says it's about changing people's habits.
He said: "It was quite hard at first to get people to switch off all the time but now we do it without thinking. I do things at home and I tell my parents about recycling."
Head Janet Hayward says the initiatives are also aimed at the community.
"Two of our parents sit on the eco-committee and one of our dads managed to get us some recycling bins so it's about spreading the skills in the community," she said. "Our work is also on our school noticeboard."
Turning off the lights when leaving a room may sound obvious, but recent figures show pound;450 million is spent annually on energy in UK schools - three times as much as on books.
Barry Island's eco-committee now plans to reinvest the pound;350 saved on lighting into conserving water at the school.
"Our homework at the moment is researching toilet flush bags," said Kieran.
"We're also going to turn the water off on a Friday and on Monday turn it back on to see if any water leaks over the weekend."
Green agencies say every school on average spends pound;2,500 a year on water, and a large secondary school can pay as much as pound;20,000. Barry Island is one of more than 1,400 schools in Wales involved in the Eco-Schools programme that promotes sustainable development.
Just 215 schools have been awarded the prestigious Green Flag award for eco initiatives, which Barry Island is aiming for within a year, says Linsey Lewis, the eco-committee's co-ordinator.
"The pupils are all clued up about the environment," she said Helen Northmore, of the Energy Saving Trust, said: "Our daily actions can have the biggest impact - on the environment as well as our bills."
Leader, page 26