Making changes in education is not an easy thing. Most folks are fully willing to continue to participate in the status quo, occasionally questioning something that doesn't feel quite right but also doesn't feel wrong enough to actually try something different.
When we make bold sweeps to move away from time-honored traditions like grading systems - those which label kids and their work based on often arbitrary criteria, people push back.
Students will push back because it is unlike what they are used to and will find the new system in a lot of ways harder - no longer able to hide behind the game.
Parents will push back because they went to school and understand the grading system as it was and don't know how their kids can get into college without grades.
Colleagues will push back because this all seems like A LOT more work than they are already doing and as it is they don't like the grading they have to do... or do they?
Admin may push back because they don't understand but may come to be your best allies when they see the results.
Check out this short video and Hacking Assessment to know more about how combat challenges when it comes giving up grades.