Of the co-ops I've seen locally, it's very similar to what Alice and mom2att described, up-thread.
Diverging now from O.P.'s question to share what I see with co-ops in our area:
Unfortunately, what I have (repeatedly) seen with local co-ops that are strictly "co-operative" -- i.e., only parents teach classes and are not paid -- is that the co-op fizzles after 2-3 years because the parents who teach burn out, and the other parents who weren't teaching don't step up because they don't have the time or ability or desire to lead a co-op class. For many families, the reason they want to do a once a week co-op class is to get a break from teaching, and to have some social/group activities for their kids. And frankly, when these co-ops try to force people to teach, thinking it will balance the time/effort inequality, it backfires -- families just drop, or, if the parent does lead a class, they put absolutely NO effort or prep into it, and it's a waste of time and a frustration to everyone.
I think a strictly co-operative situation works well when it is limited to about 6-8 families who sit down together in advance of the year, plan out what will be happening, and everyone shares a roughly equivalent load that falls in their strong area. For example, families who are doing the science experiments together for the high school science. Or families who are doing Tapestry of Grace activities together.
At least in our area, the only co-op that has kept going for more than 3 years has been a hybrid that offers "two tracks" of classes -- everyone pays a small per-family fee to cover the cost of the facility and supplies (say, $15-35 per semester), and then some classes are free (offered co-operatively by a mom), but other classes have a per student fee (say $60-$150 per semester) that are led by an outside instructor -- i.e., someone who is not currently homeschooling and has expertise in an area. The "for-a-fee" classes give the co-op stability from year to year, while the "free" classes run by parents shift every year, depending on who is willing/able to lead a class.
I have also seen a local co-op that slowly moved from all co-operative to all "for-a-fee" fail as well -- eventually, all of the teachers ended up charging a per-class fee in order to make a little money, to the point that it would cost $400-600 dollars per semester to have 3 children in 3 classes that would have previously been offered by parent volunteers.
Co-ops are a tricky thing to keep going.
Edited by Lori D., 11 January 2018 - 04:24 PM.