You don't have to parent exactly the same way to keep a consistent schedule. It may be hard to talk to your ex (I don't know what your relationship and communications are like), but if you can share info, there may be things you can adapt.
Also, how long has this been going on? Has your son had the same visitation schedule for a while? If it's new, he may be "better" right now but not stay that way.
I'd also ask yourself if you are being to hard on yourself and putting too much stock in the "class dojo" chart. Maybe it's not that dramatic a difference between weeks. You are getting into the "I'm a terrible mother" head and that may mean you're looking at a few "bad behavior" blips and blaming yourself.
What you might do is give the teacher a head's up about your suspicions, and make sure she has the dates when your son is with you vs. with dad. Ask her if she sees a significant difference.
It's also okay if a boy bonds with his dad and wants to please him - he may be toeing the line more because he sees his father as more of an authority figure. That doesn't mean you're doing anything wrong.