The Woodland Trust is fighting Perth and Kinross Council's plans to remove a mature Scots pine from the grounds of Perth Academy in order to install a new sports pitch.
The council has refused an application by the trust to list the tree, thought be at least 150 years old and marked on the area's first ever Ordnance Survey map of 1886.
Pupils have also collected 500 signatures on a petition to save the tree, which has served as a memorial to two former pupils killed in a road accident in 2009.
Councillors will decide the tree's fate at a meeting later this month to consider the planning application for the new sports facilities.
A spokesman for Perth and Kinross Council said: "With the many other high quality mature trees around the school grounds, it is not considered appropriate to pursue a TPO in this instance."
But Woodland Trust Scotland policy manager Andrew Fairbairn said: "They seem to argue that because there are other similar trees in the area that it has no value, but anyone who has seen it will know it stands alone in the middle of the school grounds, and it has a distinctive character.
"It is easily equivalent to a listed building and should be given the same level of protection."