They're analysing data in Hamilton Grammar science classes and predicting the impact of global warming. Modern studies is assessing its effects on society, and RME is debating the moral responsibilities of looking after the planet. Over in English, pupils are writing heartfelt letters from the future.
The fate of the planet is such a huge, all-encompassing concern that it makes no sense to hive it off to a niche part of the curriculum. That's the logic of a popular resource which has inspired schools to block off up to two weeks to explore its ramifications.
Global Footprint allows schools to measure exactly how much carbon dioxide they are pumping into the air. The startling results have dramatically altered the way schools are managed, and convinced secondary teachers to tear up the rulebook on working independently of other departments.
The resource, which is available through Learning and Teaching Scotland and uses the expertise of WWF Scotland, includes six different kinds of "footprint calculators". These crunch the numbers for a school's use of waste, water, food, transport, buildings and energy.
The shock of the results can have a dramatic effect. At Markethill Primary in Turriff, Aberdeenshire, P7 pupils worked out that the school used 1,157,500 litres of water a week. They organised a campaign to reduce consumption, asking everyone to use taps only when necessary and not to turn them on full blast, while water-saving devices were placed in cisterns. These simple measures cut water use to 45,000 litres a week - a reduction of 96 per cent.
But the bigger challenge was to have an impact in secondary schools, since the resource relies on an interdisciplinary approach.
Betsy King, education policy officer for WWF Scotland, says: "It's more difficult in secondary than in primary - primaries seem to naturally work in that way, and any one teacher is able to integrate a number of different subjects. The challenges really are finding the time in the timetable."
Hamilton's solution was to block off two weeks for an S1 and S2 project inspired by Global Footprint, which would involve almost every class.
The school was already well set up for a cross-curricular project, since it had a "world view group" involving five teachers - with separate responsibilities for sustainable development, international education, health promotion, citizenship and enterprise - who met regularly and promoted interdisciplinary work.
The Eco-Schools Group began the project by measuring three main areas: gas and electricity readings were obtained from office staff to calculate the school's energy use per person; janitors helped measure waste produced in a four-day period and the proportion sent to landfill; and school plans were used to calculate the building's area.
The measurements were checked by the maths department and put into the Global Footprint calculator, which showed the 1,200-pupil school was responsible for about 340 tonnes of carbon emissions a year. Now, pupils had to work out what to do about it.
They wanted to try something practical, and came up with a carbon- offsetting scheme. This requires payments into projects which reduce carbon dioxide emissions elsewhere.
The Eco-Schools Group hit on the idea of starting a mango tree farm at a Ghanaian school with which they already had strong links. Pupils got the business department to help raise funds by persuading local companies to buy carbon credits to compensate for their own greenhouse gas emissions.
Within a few months, they had raised pound;2,000 - enough to plant 50 acres of mangoes and offset 20 tonnes of carbon emissions per year.
The impact of such ambitious projects has been impressive, Mrs King says. Attainment has risen - which she puts down to linking subjects to real- life issues that young people feel passionate about - and teachers found the project "liberating".
Sinclair Dyer, Hamilton Grammar's principal teacher of sciences, says teachers of each subject were trusted to use their expertise and tackle the theme in any way they wanted. He would never have come up with the English department's approach, of getting pupils to write letters to and from people in the future. The "visceral" responses took him aback: for example "I hate you. You had a chance to do something. You've ruined our life."
The impact of Global Footprint at Hamilton Grammar has stretched from the local and mundane - recycling boxes in every class and lights that turn themselves off - to the inspiring and international. Money has kept coming in for the mango farm, and it is now generating income itself. This, in turn, has been used to support an orphanage and a small school, called Clyde Valley High in recognition of its friends in Scotland.
The ambitious scale of the project would not have been possible without A Curriculum for Excellence, says Mr Dyer, since it has freed teachers from "ticking the boxes" of restrictive subject guidelines and released them to spark ideas off colleagues elsewhere in the school.
"It's important that you have as many people involved as you can," he said. "In the past, you might have done something like this on your own, but the fact is that we've got much more robust.
"It's not just you and your own agenda - you've got input from a huge variety of backgrounds."