Hi Geoff,
In your layout settings, you have set 'Order by Post Publishing Date'(http://take.ms/fY3mk).
This means that the posts on the frontpage will sort the blog posts according to the 'published' date(http://take.ms/DDDxA).
For example, if you compare the two posts 'How to find a private tutor' and 'Internet safety for kids'. You will notice that the published date for the former(16th Dec) is later than the latter(13th Dec), which is why the former is placed on top of the latter post.

If you order the frontpage posts by post creation date, then the ordering will follow the creation date(the date above the published date in the composer).

Hey Geoff,
Glad to know that your issue has been resolved now.

As a gentle reminder, kindly start a new thread if you have any other issue in the future so it will be easier for us to manage your inquiry. I will lock and mark this thread as resolved.