On a regular school day, four-year-old Kush Bhattacharya can leave his mathematics class to run barefoot on grass, hide from his friends in a cave made of cow dung and return to recite nursery rhymes in a red bus that doubles up as a classroom.

Kush is a student at the Aman Setu school in Pune, an educational and technological hub three hours drive from Mumbai.

Almost every part of the school premises is made out of recycled material, including roofs made out of old hoardings, walls built from plastic bottles and hand-stitched uniforms made out of eco-friendly 'khadi', or handspun, cloth.

"It isn't a marketing thing, it's what we believe and how we live," says Madhavi Kapur, who started the school in 2008 with just four students. The school now has more than 140 students studying up to grade five.

"We didn't have too much money to begin with, and one of my (former) students, who is an architect came up with the idea of using recycled materials to build the school on a piece of land leased to me by my brother," she said.

Starting off with a modest 600,000 rupees ($13,500) Kapur and architect Saurabh Phadke devised ways to build walls from mud and old cement bags. They were then tamped down and plastered with mud.

Consisting of just two one-storeyed structures which house four classrooms, students at Aman Setu, which means bridge of peace, sit on rattan mats on a cowdung-plastered floor, use text books handed down from other students and grow their own vegetables in a small garden.

Children get to feed fish in a tank, watch a robin's egg hatch and travel to school by community transport - all in an effort to make them more environmentally conscious.

Kapur also acquired an old bus from the government transport authority, stripped it down, and refurbished it as a classroom.

"We don't mind them walking out of a maths class, feeding their favourite fish, taking a barefoot walk in the grass and then coming back in. We want them to be one with the surroundings," says teacher Bano Bhagwat, as she teaches a gaggle of excited kids how to make lemonade.

It might sound like a school straight out of a fairy tale, but it wasn't all smooth sailing.

"Parents weren't willing to send their kids to a school which had an old bus doubling up as a classroom. We started off with just four students, and I've had a hard time convincing parents that it was a safe environment" Kapur said.

Now that the school has grown she has an entirely different problem persuading parents that they should not tear down the concrete building down the road -- into which they have already moved some classes -- for a more environmentally friendly structure.

"We have moved to a bigger structure down the road. But that is a concrete building, and parents don't want their kids to move there. They want me to stay here." says Kapur.

"Now, they are giving me lessons in the environment. But for me, tearing down a concrete structure is also not ecologically sound."

For now, Kapur hopes to replicate her eco-friendly teaching methods at the concrete school as well, with plans for a rain water harvesting facility, a vegetable garden, and of course, a fence made of old plastic bottles.'

"This is a way of life, we plan to continue it no matter where we go," she says.