Hi alzado,
Copyright or patent attorneys are specialists. If you read all the material you suggest - surf the web, read FAQ's, parts of Circular 92 etc. - you will be much better prepared to talk with an attorney by knowing the meaning of "public domain", "fair use", "Title 17", why 1923 is an important year, etc. An attorney can tell you if a law has been tested in court, how cases were decided recently, whether there is new legislation, etc. This information might be critical, and reliable sources are not normally available elsewhere outside law libraries. I've gotten free telephone consults in simple cases, and it's U.S. Federal law, so a U.S. telephone call may be all that's needed - the attorney doesn't necessarily have to be nearby. It can be a hit or miss proposition to find one that's available for a few minutes when you ring their telephone. If nothing else, they can verify that you are looking at applicable parts of the law. Finally, "fair use" isn't a precise standard. So, if you want to be certain - don't copy at all, as suggested above.
Since teachers are frequently in contact with impressionable young people, it's important to avoid any implication of illegal behavior, however unintended or seemingly inconsequential. The whole area of copyrights has become quite important in music, particularly, because of the internet and other computer technologies. Anyone in this forum should have some concern about such matters, not only to ensure the supply of material, but also to ensure the possiblity of fair compensation for their own original works and that they aren't entrapped by someone else's recklessness.
Regards,
Jim Ritchie