When we started rotation 7ish years ago, we had the same problem...we did a couple of things that work beautifully!
SHORTER ROTATIONS: We started rotation for 6 weeks and found that just was way too long, so we played with it for a couple years and are down to FOUR weeks per rotation. Teachers will commit to FOUR weeks...and if they don't, no big deal.
EASIER LESSONS: Our lessons are so easy to follow that anyone can jump in and sometimes with busy schedules we have that happen where a teacher can only be there for one week out of the three. We have a few folks on standby who jump in. Last week a teacher was late and the lesson plan was so easy that the shepherd just took over. Worked great and he even commented to me how easy and straightforward it all was. Piece of cake!
MORE HELP in OTHER WAYS: We created and passed around "Hey Everyone Let's Participate" sheets asking each and every single parent to do something. They HAVE to pick at least one thing they can do - teach, shepherd, help with Living Last Supper, Movie Days, bring snacks, supplies, etc. We get huge participation on that. We ask for email addresses and then contact them throughout the year when we need to do things.
SIMPLIFIED TRAINING and MORE PREP "FOR" TEACHERS: We made it easier to teach by having a small team do more of the lesson supplying and workshop setup for the volunteers.
LESS WORDY and LESS THEORY: We dropped some of the intimidating explanations and expectations for certain workshops. Now we have a format that no matter who you are, if you are a seasoned teacher or not - you can walk into the classroom, grab the folder and teach with minimum prep. In this folder (made up for each workshop leader) is a Common Threads Sheet that includes the memory verse, tips on teaching, objectives, opening prayer and story. Then each folder has the Workshop Discussion and Activity. All crafts are set out ready to roll with a sample...same with all the workshops. Everything is set up and the teacher just has to show up.
BREAKS IN THE SCHEDULE.
LEAD TEACHERS: Another thing that we did when we started is we had a seasoned workshop leader work with an "assistant" so they could listen and learn.
CHANGES: Instead of every year being the same, we changed up some approaches, workshops, even teaching. Most recently, we have had some of our 9th grade students teaching the workshops and are finding that these kids love it, too. They are developing leadership skills, and the younger kids truly look up to the older ones.