Airthrie's class structure is possibly a unique system.  For many years at Airthrie each age group and class has been named after a tree and instead of a House system all pupils are divided across the age range into four 'Forests'.

The very youngest pupils of just three years of age are known as Little Acorns whilst the next age group of rising four to five are Big Acorns.   These pupils comprise the Airthrie Nursery.

After this a variety of (usually British) tree names are used to identify each age group until the last age group and oldest pupils are described as Oak.