I thought that was automatic. I get a red line under everything I spell incorrectly, except the mistakes like those in the first post which are not picked up. I have Windows 8, maybe it's automatic.
The Americanisation is a frustration though.
His previous posts are more than readable. He may be quite young, but at no stage would I assume or suggest learning difficulties. In fact, hearing that would probably make him feel far worse.
I often have to correct my spelling of words like 'there' and have even put 'are' instead of 'our'...