Commas in lists

Compare these two sentences:

  • Some of my students use commas, hyphens, and full stops incorrectly.
    Some of my students use commas, hyphens and full stops incorrectly.

In the first sentence there is a comma after the word hyphen but not in the second sentence. This is called an Oxford comma. It is a comma that comes before the final item in a list.

Both sentences are correct, but you need to decide to use it all the time or never use it. Don’t mix your usage.