I read, with interest, the story on Gotham about the Principal of Truman HS who gives diagnostic tests to incoming students because she doesn't trust middle school Grades. Packemin does the same thing and, from experience, I don't think this is the answer either.
Many incoming middle school students don't take those placement exams seriously. I had a group of boys one year who decided to see how many letter patterns they could make with the choices. They found this far more interesting than the math questions they were supposed to be answering. All the boys were bright, their middle grade scores were high, yet they ended up in a low level class based on this exam. I've had other students forced to repeat classes they did well in because they diagnostic exam came on an "off" day for them. Many were angry at being placed back and never reached their full potential before graduating. I once found a brilliant girl in a low level class due to this placement exam and managed, behind my AP's back to get her out. By the time this young woman graduated, she completed AP calculus and is now doing very well at Sophie Davis Medical School.
Jose Vilson, one of my favorite bloggers is a middle school math teacher has written about some of his top students not doing well in high school due to the high school education. There are plenty of good middle school teachers, like Jose, who do a great job of preparing students and their grades should not be ignored.
There might be inflation of middle school grades but I don't believe a high school, or any school for that matter has the right to discount the education students got there I also don't believe a student's education path should be set by one placement exam.
Packemin worries about statistics, as all schools do. They don't want to risk putting kids in classes they might fail. Truman, like Packemin, might be doing more harm than good.