I find this thread interesting. I was educated in a 'special' school. Mainly because of a physical disability. We were also bunched in with people with other disabilities, like the blind, the deaf and people with mental conditions.
This meant that the level of education I received was barely up to GCSE standards. I have always tried my best when it came to spellings, punctuation and general grammar. I know that as always been my weak point though.
Being a technical mind, is there a simple page that gives examples of when to use what apostrophe?