Work Meeting Aftermath

I oversee the science department in a school district. We have department meeting times each month for 1.5 hours. One of our district goals is to create benchmark assessments (common tests the teachers can use to see what students know). I wanted to get teachers to buy in as part of the process so I involved them in determining what is important to test kids on. The feedback today (after the meeting) was that it was a waste of time, etc. I thought it was an important step, but the teachers didn’t see it that way. They also don’t see eye to eye with each other. I’m struggling with how to move forward from here. The teachers are also accustomed to doing their own thing. This seems like a fruitless effort; I’m not sure how to move forward and appreciate the teachers’ feedback. I’m struggling with how to take it in (especially when it differs from teacher to teacher) and make it usable, and not lose sight of the end goal of creating common assessments. I am hating being a middle manager right now.