EDUCATION ranger Denise Cox holds up a slug (see picture below). "Look what someone has found. What can you tell me about this creature?"
Her questions were met with squeals of delight as the children, aged eight and nine, gathered round for a closer look and offer their knowledge of slugs.
"They have antennae."
"They leave trails."
Looking on, Jo Phillips, parks education officer, smiled.
"This is the reaction we love. The children are excited, having fun, and learning about nature in this wonderful environment."
I joined a party of about 75 pupils from St Thomas of Canterbury Junior School who are spending the day at Thorndon Country Park. Their aim was learn more about the park's wildlife, their habitats and how seeds are dispersed.
In order to do that they were split into three groups and each allocated an education ranger who led them to different parts of the 500-acre site. The children were encouraged to get their hands dirty, and the activity was guided by their discoveries.
"And, you'll notice," said Jo, "there's not a clipboard in sight. Children don't pause to take notes, they spend the whole time here exploring the environment, and save the writing up until they get back to the classroom."
Jo oversees the education programmes run at Thorndon, and its six sister parks, which includes Weald Country Park.
Themes range from the mini-beasts and habitats, survival skills and geo-caching, to The Gruffalo, Pirates and Dinosaurs for younger children and Michael Morpurgo's Kensuke's Kingdom and Charlotte's Web for youngsters aged eight and over.
Bringing the teaching of a book outdoors is one of the innovative ways Jo and her team use to encourage schools to come back to the parks year after year.
And it is obviously working.
With the number of pupils visiting the popular leisure spot increasing each year, teachers are clamouring to book a day from their range of activities, which cover almost every area of the curriculum.
"We have designed the day to suit both the class and the teacher and made it as cross-curricular as possible. Every visit has a large element of numeracy and literacy. Communication and language are also high on our agenda, but best of all they are being taught in marvellous places that inspire creativity from every child. In March 2010, 280 children visited our parks – this March saw 2,000."
By this autumn the rangers are expected to have taught about 10,000 children from not only Brentwood but mid-Essex, Havering, Thurrock, Kent, central London and Hertfordshire.
Amanda Wellington-Bovis is one of 11 education rangers who work across all seven parks. In the meadow area of the park she has picked out pupils Layomi Mustafa, Emily Eyo and Alex Banfield to pretend to be trees and demonstrate how seeds are dispersed. Using drama is one of the ways the rangers combine all curriculum areas.
The daughter of the manager of Belhus Woods, Amanda grew up in a country park and was a volunteer from the age of 13. She said: "You could not do this job unless you enjoyed it and were able to get the message across in a fun way.
"We have a zero-hours contract, so we work as and when but the increase in demand means I'm working nearly every day.
"We also start much earlier in the year – we had several visits in February and will probably carry on well into November."
Back in the woods Denise asked the youngsters to find materials to make a nature art picture.
They collected ferns, twigs, leaves, grasses and in doing so uncovered menagerie of mini-beasts.
Lauren Hastings, 8, said: "We have found slugs, centipedes, and beetles, and these other things which I don't know what they were called.
"I like it here, it's fun."
Alex Murchie, 8, added: "We have been lucky to see slugs, beetles and centipedes. They weren't that hard to find."
Down by the pond, education ranger Clive Hopgood was leading a pond-dipping session, looking at the habitats of creatures living in or near water.
Libby Wright, 8, said: "Before I came today I did not know what pond-dipping was. I found this little wriggly thing. We found several tiny creatures.
"You had to look very closely as they were really small."
Tara Duffy, 8, said: "In my group, we found this big leech and a newt; it was a grown-up, the ranger said.
"We also caught a skin that had been shed by another creature."
The 11 rangers, who mostly work on a part-time basis, come from a range of different backgrounds. Some were teachers but most were not.
Jo explained: "Every visit is unique. Although we have a set programme, the education rangers are free to adapt them to suit the age, ability and curriculum requirements of the children in each group.
"They are also encouraged to be as creative and spontaneous as possible. When we plan the day, we ask: Can you do this in a classroom? If the answer is yes, then we don't do it.
"We are not teaching just the children but also the teachers, so they can replicate the experience in a location closer to their school, in the actual grounds or a local park or garden.
"If everybody leaves thinking they have learnt something, regardless of their age, then we have done our job and accomplished what we set out to do – which is to create a memorable experience."