Couldn't help but notice Ocifant's posting re the Menear Longstone from way back in 2003. The description and photo seem to actually relate to the Gwallon menhir in Penrice School (those are the right blue uniforms in the photo).
Anyone else confirm this??
The Menear Longstone actually stands in the field next to the local recycling tip, opposite side of the road from the small reservoir and mast, directly behind Menear Farm itself, just off the A391 out of St Austell.
It isn't listed on the ordance survey but I make the map ref approx:
Latitude: 54° 50' N
Longitude: 03° 40' W
Went up there today to bag a photo but there seemed to be a late crop starting so reluctant to trample it. I'm posting the poor effort I did manage but will upload something better later in the season.