The following are some common errors that I see in papers that are turned in to me.  E-mail me if you have any questions.

· Usage of semicolons - The clause after the semicolon should be independent, i.e. have a subject and a verb.  Often students put a fragment after the semicolon.

· Misuse of apostrophes -   As or 1950s, not  “A’s” or “1950’s.”  Also plural nouns don't need an apostrophe:  "I hope all my students do well."  Often students put an apostrophe between the "t" and the "s" in "students."   Update - I formerly had "M&M's" on this list, but I've discovered that it's a trademark and I assume the possessive form is due to belonging to the Mars company . . . or could it be years ago someone made a mistake?  Hmmmmm . .  . .

· Subject/pronoun disagreement -  Here’s an example that’s incorrect.  “Every child should use their brain.”  ‘Child’ is singular, but ‘their’ is plural . . . plus it sounds like children together have one brain!  “Each child should use his or her brain” would fix the problem.

· Capitalization of letters for subject titles, but not for general subjects -  Examples are “Algebra I” because that’s the title of a course, but it should be “I took several algebra courses.”

· Misusing “its” and “it’s” -  The first one shows possession, while the second is a contraction.  “The dog hurt its paw” and “It’s almost time to go.”

· Misuse of “principal” and “principle” – “The principal of the school is a good guy” and “The principal reason for learning algebra is to aid in problem-solving.”  “We’ll learn the Fundamental Counting Principle.”

· Misuse of “your” and “you’re” – The first shows possession and the second is a contraction.  “I like your hair” and “You’re going to be late.”

· Mixing up “their,” “they’re” and “there” – “Their project was exceptional” because “they’re such good students.”  “I would love to go there” or “There should be a law about that!”

· Leaving out the hyphen when a phrase is used as an adjective – “I think it’s important to do hands-on math” or “He is a sixth-grade student.”

· Run-on sentences and sentence fragments – Many times students use a comma when a period or semicolon is needed.  Examples:  Jake is a great dog; however, he often misbehaves.  (It would be o.k., though, to say, "Many dogs have behavior problems.  Jake, however, is a great dog!"

Here are a few more that have come up:
Using "that" when "who" sounds better, i.e. when referring to a person:  "The teacher who made a big difference in my life was Mrs. Jones."
Making homophone mistakes, i.e. using "knew" for "new."
Putting periods and commas outside rather than inside quotation marks.
Misuse of "everyday" and "every day."  Use it the first way when it's an adjective:  "It's an everyday occurrence."  Use it the other way when describing time:  "My teacher uses manipulatives every day."
The word is "definitely," not "defiantly" when used in a sentence like this -  "I will definitely use manipulatives when I teach math."
It's "of course," not "of coarse."
Ending a sentence with a preposition
"hands-on" and "problem-solving" should have hyphens when used as adjectives