Even if we accept that premise, the failure of those "best teachers" to convey measureable knowledge to the students would mean the teachers were NOT "highly effective." "Effective" means "achieving the desired outcome."
Of course, this raises the question of what is the desired outcome for Detroit teachers. We're only assuming that conveying measureable knowledge to the students is the goal. I'll bet 80% of Detroit teachers are highly effective at paying union dues, agitating for Democrat causes, using students to agitate for Democrat causes, concealing the financial misdeeds of administrators, and so on.
I see. If producing kids that don’t know math or reading and can’t write means “highly effective”, then the grades were gimmees.
You are both right. My wife teaches in a school where many of the kids come from single parent households and many are brick stupid. There is a group of teachers in that school who attempt what I call polishing a turd and do their best to work with the dummies. My wife in particular has a reputation for dragging kids over the passing line for standardized tests. Do they succeed in imparting knowledge, results vary, but I would defy someone to do better. OTOH there are many teachers who are just there for the paycheck and do little more than house the kids for 8 hours.
If I saw that two or three in 10 teachers received the highest marks, even in a horrible district, I would believe it. 8 in 10 means they are not properly evaluating.