Grammar Peas...please answer this!

I would write Chris' as we were always taught in school that words ending in s didn't need the extra 's for the possessive. But I've seen both recently and I'm pretty sure the UK uses 's in those cases.

Per my 5th grade teacher, both are acceptable. I usually use Chris'.

You could use the mental gymnastics that would be 'the item belongs to Chris' to avoid the question altogether.

ETA: I just that the teacher marked it wrong? Would your daughter feel comfortable talking to the teacher to find out why she thought it was wrong? Back in the dark ages, the only answer that would have been right would have been Chris'.

My younger DD's name ends with s so I remember checking years ago. Both are correct although not everyone realises that and will assume it's wrong if you don't use another s- clearly!!

The first one is correct.

What is APA Style? If either of the As in that acronym stand for "American", then I'll just ignore the rule and continue happily on with my use of Chris'  !!   

Both are accurate, but depending on the schooling of that particular teacher, he/she could have learned it as Chris's. I would politely ask the teacher at a later time. As a previous teacher, I found that parents learned things differently than I had and sometimes both ways were perfectly acceptable. I taught my classes to just drop the second s.

Truth be told, the academic writing styles mostly focus on how to cite research sources...so lots of emphasis on bibliography formats, endnotes v. footnotes v. in-text notes, etc. Within an academic field - say, Anthropology - dissertations and journal articles will use the same citation style, which a helpful to readers and other researchers. 

A handy chart. I have no idea what the rest of the world uses. Maybe there are some academics here who could chime in. 

The academic style books do also cover things like grammar and punctuation, but for the average Josephine writing a report for work or a newsie article for company publication, they'd probably look that kind of stuff up in Chicago or AP.

I would always write Chris's, and that's how I would say it too. If I said "Chris' book" I would think that meant a book belonging to Chri!

Chris's. He is not plural which is when the apostrophe comes after the s.

There is a long-standing tradition of apostrophe-only with proper nouns that end with S. The Associated Press style book still recommends it and many newspapers do it - as do, apparently, a lot of Peas! So, neither way is necessarily wrong; it just depends what tradition or style you follow - or which one your school or company espouses. 

I haven't looked it up in a while, but I believe "Chicago" used to go into a whole song and dance about whether the ending S makes an "s" sound or a "z" sound. 

Related: you almost always see < Jesus' >. The Catholic Church has a style rule about it. (I've done some proofreading for Catholic publications.) 

~AmeliaBloomer
Pedant 

Here is more than we could ever want to know about possessives on proper names ending in "s"

(TL;DR: we are all right and wrong )

Answer: Radio and television announcers pronounce words the way those words are written by news writers. News writers follow conventions in style manuals that are written to match the preferences of the audience for that medium. Most news writers follow newspaper-style conventions, which are set out in, for example, The Associated Press Stylebook and Libel Manual. The AP recommends that possessives of proper names ending in "s" be formed by adding an apostrophe only (no extra "s"). Thus, in AP style, the possessive of Jones is Jones'.

Different style manuals handle this in different ways. The Chicago Manual of Style, which is the manual for book editing, recommends that most possessives of proper names include an extra "s." It makes exceptions for Jesus, Moses, and names of more than one syllable with an unaccented ending pronouned "eez." Thus, Euripides', not Euripides's.

Spelling conventions are in some sense an attempt to replicate pronunciation. When style manuals make pronouncements on spelling, they imply that the presence of an extra "s" means that most educated speakers customarily pronounce that sound. The reason that this system cannot simply be reversed to produce pronunciation rules is that style manuals are directed at written language, and they are thus also interested in visual consistency and eliminating visual distractions.

In short, it is not possible to look at the spelling of a word and make safe assumptions about common pronunciation. The system goes from pronunciation to spelling—not from spelling to pronunciation—and there are many other variables at play.

Nevertheless, the best of the style manuals (q.v. The Chicago Manual of Style) give at least ambient advice on this point. Here's Chicago's rule 6.30:

How to form the possessive of polysllabic personal names ending with the sound of "s" or "z" probably occasions more dissension among writers and editors than any other orthographic matter open to disagreement. Some espouse the rule that the possessive of all such names should be formed by the addition of an apostrophe only. Such a rule would outlaw spellings like "Dylan Thomas's poetry," "Roy Harris's composition," and "Maria Callas's performance" in favor of "Thomas'," "Harris'," and "Callas'," which would not commend themselves to many. Other writers and editors simply abandon the attempt to define in precise phonic or orthographic terms the class of polysyllabic names to which only the apostrophe should be attached and follow a more pragmatic rule. In essence this is, "If it ends with a z sound, treat it like a plural; if it ends with an s sound treat it like a singular." Thus they would write "Dickens', Hopkins', Williams'," but also "Harris's, Thomas's, Callas's, Angus's, Willis's," and the like.

Thus, no one can give you rules for the pronunciation of any (and all) words of a given type, but it is possible to get answers (or at least opinions) for specific examples.

Witness's, for example, is formed from a common—not a proper noun. All style manuals agree that it should be written with the extra "s," and I am willing to say that most educated speakers pronounce that "s."

Jesus' (along with Moses' and names of more than one syllable with an unaccented ending pronounced eez) is among the traditional exceptions to the general rule for forming the possessive. There is no extra "s"—spelled or pronounced. The Chicago Manual notes that this practice began "for reasons of euphony."

Jones in the possessive is harder. The AP Stylebook tells you to add only an apostrophe. Chicago tells you to add "'s." Chicago's more complicated rule 6.40 produces "Jones'" because Jones ends with a "z" sound. This latter rule is the only one truly based on pronunciation.

The Grammar Hotline recommends witness's (spell and pronounce the extra s), Jesus' (neither spell nor pronounce the extra s), and Jones's (spell and pronounce the extra "s"). The last of these is the only one I am not sure about. A variation in that form would be acceptable if it were treated consistently.

www.ncsu.edu/ncsu/grammar/Apostro3.html

Oh, contraire! They use apostrophes all the time to form plurals.

I mean plural's.

According to the AP Style book (2011) a proper name ending is "s" only gets an apostrophe.
There ARE other nouns that end in "s" that do get an extra "s" following the apostrophe.