Mary,
Well spotted!
I had created a badge and selected 'Teacher' as awarder BEFORE following the FAQ and creating the 'Site Badge Awarder' role.
I've gone back to the badge settings and changed from 'Teacher' to 'Site Badge Awarder' and all works as it should.
Thanks for your help.
Pete
PS One other bit about the FAQ - You say in step 2 'Add it to the System context' which is fine but you don't mention what setting to give for the Role Archetype.