When it comes to teaching punctuation, commas play a far bigger role than their size would suggest.

Six of the 20 most common errors in student writing involve comma usage. That's the bad news.

The good news is that those six errors occur in very clearly defined, specific situations that rely on a tacit knowledge of grammar all native English speakers have.

That means you don't have to teach the relevant comma usage rules to people whose native language is English.

It also means that teaching punctuation requires you to help students discover what they already know about English grammar before you tackle teaching punctuation.

Students whose first language was not English need to be taught by some other method. You can't expect them to have picked up English grammar in a household where the spoken language was Urdu.

Reasons for the top comma error

One extensive study found the single most common error in student writing (aside from misspelled words) was failure to put a comma after a long introductory element. The rule causes problems for one or more reasons:

• Students don't know there is such a rule.

• Students are confused about how long an introductory element must be to require a comma after it.

• Students don't recognize an introductory element.

• Students don't recognize a sentence.

In teaching punctuation, you can address all of those areas by working on the last one: sentence recognition.

Begin with sentence boundaries

In teaching punctuation, you can use some of the same techniques you used in teaching students to identify subjects of sentences.

The tricks for finding the boundaries of a written sentence provide a way of teaching students to identify the introductory element.

Introductory element defined

An introductory element is a pre-sentence or before-sentence modifier. It is not part of the complete sentence. It appears at the left of the complete sentence.

The other other really important thing to know about introductory elements is that they could be moved to some place within the sentence and still have the sentence make sense.

Let's simplify this even more:

An introductory element is a modifier at the left of a complete sentence that could be put inside the complete sentence and still have the sentence make sense.

Test for introductory elements

To find out if we have an introductory element that needs to be set off by a comma, we have to see

• If we have a sentence, and

• If something ahead of the sentence can be moved inside the sentence and still have the sentence make sense.

Remember the yes-no questions we used to identify the sentence boundaries? They will also identify introductory elements when you are teaching punctuation rules to your beginning writers.

Here's what to do:

1. Use the tag question and the yes-and-no question to find the boundaries of the original sentence.

2. Move anything that was ahead of the original subject to the end of the original sentence.

In each of the sets of sentences below, A is the original declarative sentence, B is the tag sentence, and C is the yes-no sentence.

Example set 1

A (Original). First Kathy got out the ladder.

B. First Kathy got out the ladder, didn't she?

C. Did Kathy get out the ladder first?

In this set, the yes-no question (C) suggests that the word first can be moved from its original position without changing the sentence meaning. We can test that hypothesis by rewording the sentences again, like this

B2. Kathy got out the ladder first , didn't she?

C2. Did Kathy get out the ladder first?

All those sentences make sense, don't they? That means the word first is an introductory element in that sentence. It can be moved inside the sentence without messing up the meaning of the sentence.

Do you see how teaching punctuation based on basic grammar knowledge and some common sense put correct comma usage within the ability of nearly every student?

Example set 2

Try to frame a tag and a yes-no question for this statement.

A (Original). In her excitement Maribeth failed to notice the cat.

You'll come up with statements like this:

B. Maribeth failed to notice the cat in her excitement, didn't she?

C. Did Maribeth fail to notice the cat in her excitement?

Example set 3

As soon as you find the left hand boundary of the sentence, everything else falls into place, as in this example:

A (Original). Before the noon whistle sounded Kathy finished putting up the storm windows.

B. Kathy finished putting up the storm windows before the noon whistle sounded, didn't she?

C. Did Kathy finish putting up the storm windows before the noon whistle sounded?

It is fairly easy to spot the introductory element in each set when you use the tags and yes-no questions, isn't it?

But what happens if you think something is an introductory element and it is really an essential part of the sentence?

Example set 4

If you mistake a part of the sentence for an introductory element, you'll pick the wrong left hand boundary for the sentence. After that, nothing will make much sense, as these examples show:

A (Original). For Abraham Lincoln to win the 2008 presidential election was impossible.

B. Presidential election was impossible for Abraham Lincoln to win the 2008, didn't it?

C. Did presidential election was impossible, for Abraham Lincoln to win the 2008?

Let's try that again:

A (Original). For Abraham Lincoln to win the 2008 presidential election was impossible.

B2. Abraham Lincoln to win the 2008 presidential election was impossible for, didn't he?

C2. Did Abraham Lincoln to win the 2008 presidential election was impossible for?

There's some wrong there, too, isn't there?

The only way you can fit either the tag or the yes-no questions to the original is this way:

A (Original). For Abraham Lincoln to win the 2008 presidential election was impossible.

B. For Abraham Lincoln to win the 2008 presidential election was impossible, wasn't it?

That tells us that the original sentence begins with the word for. Since there is nothing to the left of that word in the original sentence, there is no introductory element. There's no need to apply any comma usage rules.

Tags & yes-no help with other rules

Other basic comma usage rules where teaching punctuation via tags and yes-no sentences works are:

• Place a common between independent clauses in a compound sentence.

• Don't join two independent clauses with a comma.

Of course, there's more to teaching punctuation than teaching three comma usage rules. However, if you can get students to see that they already know a good bit of grammar, you save a great deal of wear and tear on their nerves and yours.