I've always agreed that creationism could be mentioned in a social study class during a lesson plan on world religions. However, this won't be taught as "this is how it happened", it would be taught as "this is what X believes".
There are still a couple problems with this, though. I've never met 2 creationists that believe the same thing or interpret their creation mythology the same way. The mention would still have to be generalized -- simply stating that YECs believe in a 6-day creation while more liberal denominations of Christianity either see it as allegory or try to relate "day" to a long time period.
Additionally, even after you consolidate the numerous Judeo-Christian interpretations into 2 general groups (YEC and OEC), you still need to go over the creation stories of the other major religions. For example, in Islam, you have almost the same story, but I'm not aware of any mention of the time it took God to make everything. IIRC, Muslims believe Allah just did it all at once with one word. Hindu's believe that Vishnu instructed Brahma to create the world. Then you have the Shinto and other creation stories.
Teaching things about creationism, at this point, with it's diverse origins begins to look more like a separate college course, since you can't really cram it all amidst a high school class on world religion.
One thing constantly overlooked is that the bible creation story isn't the only one floating around out there and neither is there just one version of it.