Learning Conversations

I've just come across Learning Landscape for Schools - which states it's a safe social network. They do seem to have covered all the bases around security & internet safety; their registration procedures are quite rigorous.

The site is based on the open-source Elgg software - as used by University of Brighton and Rucku (a virtual clubhouse for Rugby players)... Elgg has a robust development & support company behind it, so it's a good choice.