So the teacher gives students better grades and easier work and the student stays in school and bingo the teacher is an effective teacher. Sounds like a great idea.
The poster you quoted had it wrong:
-You can compare the student's grades on standardized tests that your entire state does, so you can compare them to your district, state, different classes, and the school
-You can then go back and compare the improvement of your students from one year to the next (this is because some kids will naturally be better than others, so it's more important to measure how much the teacher is improving the student's ability).
-Teachers get evaluated in the classroom by their principal, APs, and by their district (I get evaluated quite often)
-There are ways to tell what teachers are effective and which ones aren't. If a teacher is a teacher that just gives out "easy work"....their students are going to bomb their standardized tests (or finals, as my district does), and it's going to look bad for the teacher.
-I disagree with dropouts. I had two students dropout this past semester. One kid (openly admitted) to being a drug addict. He showed up to school just to sell drugs. Never did one ounce of work in my classroom and was a pretty big distraction to all of the kids in class. Once he was gone the other kids learned a lot more. The other kid never bothered to show up. In the first semester (18 weeks) they showed up twice. Yes two times in 18 weeks.