Does the word including count as a sub clause i.e. it will need a comma.

I have worked in education for two years, including six months at St James' 6th Forum.
This is one of the most common judgement calls a writer must make, Dmilton. You may use the comma or not, depending on how restrictive you consider the phrase to be, i.e. how critically you feel it needs to be included in the thought expressed in the main clause.
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This is one of the point that I too have a problem with. What I feel is that

Oxford Advanced Learner's Dictionary gives defines "including" as "having something as part of a group or set" and gives the following examples:

1. I've got three days' holiday including New Year's Day.

2. Six people were killed in the riot, including a policeman.

There is one more in the same page under "Usage notes":

3. The website has a variety of interactive exercises, including matching games, crosswords and quizzes.

But whenever I encounter the word "including" I tend to insert the comma. The reason is that the words/phrases that the word "including" is some additional information/an important information that affects the flow of the sentence and also that the words that the word "including" introduces are not an all-inclusive list (as in the above examples; though "1" does not carry a comma, for which I'm finding the answer for).

But see the below sentence:

The G8 countries including France , Germany , Italy , Japan , the United Kingdom , the United States , Canada, and Russia participated in the G8 summit held at New Delhi.

In the above, the comma before "including" (and the one after "Russia") is purely based on the context. If the writer feels that the intended audience of this sentence do not know about the members of G8 countries, he can make it defining by not inserting the comma before "including". If he feels, the readers know he can set of the phrase within commas. Please note here the word including introduces a all-inclusive list.

Awaiting further discussion on this and also the reason why the comma is not used in the first example!!!
I have said all I have to say on the matter. I don't see that it is worth discussing further. The comma is too arbitrary to worry about. It will not affect effective, competent English communication.