have saw similar questions come up multiple times at... www.moodle.org i do not remember direct links right off, but little time searching site should bring back half dozen or more forum threads to read through, for different opinions.
their is a few folks their that belong to "open source" schools per say. and might help you find a lead if you are looking more of open source doing. so you can join in and help out vs trying to come up with something yourself from scratch.
remember being in school, and teachers having a couple "teachers books" from different companies due to errors / issues with one vs another. and their were a few times both in K-12 and in collage. teachers complaining about the "agreements" they had to sign.
you need to remember... it is not clear back in the olden days, when there was not internet. and students would sneak over and grab an answer sheet from the test book. and do a quick glance at it, when teacher was not in room / busy talking to other students on opposite side of them. heck students most still likely still do this :/
but rather today... text books "student version" and "teacher version" are more or less exact same copies of each other within there given version. nothing random in order or questions that show up in them. all it would take is one teachers slip up in any school. and a student could look up information online and easily cheat. WOOPS i had this homework, WOOPS it is done, i did not actually do home work though ughs
other words... re-phrasing of questions, different questions, even true/false questions. they need to be different. so as no easy cheating. making it difficult enough for students to cheat. so they actually do homework and/or study.
while teachers are already busy, as is, text book companies are trying to hold on to their work. in today age of times. it could be easy for someone to grab a book and just start inputting stuff into the internet or document. just like illegal downloading of music / videos / games and like. books are illegally scanned in and shared across the internet.
it has happened, not enough books to go around. more than likely someone forgot book, or still waiting for more books to come in (beginning of semester), and teacher just copies some pages from one student book. to hand out to remaining students. (see illegal downloading on internet)
there is only so many ways you can write up X + Y = 4.
for books and testing students actually reading the book, there may be more than a few questions that could be asked differently up to a certain point. pending on how many pages student was suppose to read. and/or trying to get student to think about how the book plays out.
moodle for example more likely able to take in 1,000's of questions about a book, and detailed about each page of the book. and randomly spit them out to the student within a range of pages student was suppose to read. if you got your questions from a third party that you had to assign an agreement and/or questions/answers copyrighted. you are tied to that agreement / copyright.
if questions/answers from third party source are copyrighted. and you and/or others. added in additional questions and left them open source. those additional questions i would think would be ok to keep open source. just not the questions you got from third party that are copyrighted.
how ever if there was an additional agreement beyond copyright. (seems over board), but you might be limited in being able to share extra questions pending on the "agreement" you signed. it would be assumed the question shared with all but answers shared among teachers only.
pending on school, you may have some sort of "ethics" aka laws/regulations you may have to abide by. schools are paying teachers, to teach and do there job, not mess around doing something other while being paid. and the schools most likely do not have enough funding to pay a teacher to do something else. schools pay publishers to come up with stuff, to make it easier for teachers to teach.
while above most likely does not answer your question/s directly. perhaps gives a little huh? to long over done lawyer talk in the "agreements" teachers need to sign for the "teacher versions" of books.
to note it. i am for "open source", but generally it comes down to, good old fashion hard work of blood, sweet, and tears, of producing original work. that you choose to make open source, and in that not copying something else. or less it is open source, and agreeing to the "open source agreement" in how information can be exchanged.