The pre-school at Flitch Green primary school in Little Dunmow opened last September. It joins two other Montessori settings on primary school sites in the county which have also been graded outstanding by Ofsted - St Thomas More Montessori Pre-School, in the grounds of a Catholic primary in Saffron Walden, and Maynard Montessori at Stebbing primary school, the second state primary to adopt Montessori methods.
Pre-school owner Michele Wisbey also runs Westwood Montessori in Thaxted.
Flitch Green and St Thomas More have recently been awarded a Sure Start capital grant for new buildings in the school grounds.
Flitch Green is a modern eco-school and the new nursery building will be an eco-nursery with a sedum roof, solar panels and rainwater collection.
Ms Wisbey said she has been approached by other primary schools who are keen to open Montessoris in their grounds.
She said, 'Transition and settling in is never an issue. Montessori children are more independent and get used to the school in bite-sized pieces.
'Montessori on its own isn't the answer,' she added, but running the nurseries in partnership with the schools was key.
At St Thomas More, children attend events in the school and share their lunchtimes every day with reception class and Key Stage 1 children.
Mary-Jo Hall, head of St Thomas More, said that teachers had noticed a 'phenomenal' change in the transition for children who moved up from the Montessori into reception.
'The children coming from the Montessori settled into school very easily and didn't find school daunting at all,' she said.
Teachers also remarked that children from the pre-school tended to have better motor skills.
The reception class is now using some of the Montessori ideas and equipment to help children who do not have a Montessori background.