The apostrophe has a wide range of uses within the English language. Forming plurals, however, is not one of them.
Many people, especially those that speak English as a foreign language, tend to make this blatant mistake. Here are some examples illustrating this punctuation error:
According to the rule’s we should follow him.
The waiter turned and asked, “Is that your’s?”
The boy’s were going to the school.
The confusion probably comes from the possessive use of the apostrophe, as in “The boy’s school is right after the corner.” This sentence refers to the school of a single boy. If we were talking about more than one, it would’ve been “The boys’ school is right after the corner.” Either way the usage is correct because the apostrophe is being used to show possession and not to form a plural.
Some authors argue that the apostrophe can be used to form plurals with abbreviations like CD’s and PC’s or with words that are rarely used in the plural form like but’s and if’s. Others consider it as a mistake nonetheless.
Regardless of this exception, if you want to stay out of trouble remember this simple rule: the apostrophe is not used to form plural’s. I mean plurals!