"If the child never made it to your classroom, then whose fault is it? Who had a performance dip?"
Speaking as a parent of three grown up DDs (well one is 16) and five grown up step children, it isn't anyone's fault if things go awry in the teenage years.
My middle DD was a nightmare (as a result if her Dad's death), her social life affected her final school years, the school she transferred to, helped her to turn it around, but it couldn't be measured, or the previous school blamed.
We all dispared that my youngest DD's school was closed, it had very poor Ofstead reports, but they did a marvelous job to set those up in the Unit for pupils with additional Needs ( my DD was one) to achieve success in senior school.
Likewise they were set in one if the roughest catchments areas of Liverpool, there were arrests of parents and armed fights in the playground, as well as at a few school plays, just to show what the school was up against.
Drug use was the norm.
Children are unpredictable in their nature, families hit lots of problems, which affect everyone, as they are not machines.
I dislike the set up now, we're all pupils are not given a chance to sit GCSE's this proposal will cause even more children to have to be pushed to the sidelines, so not to bring down "performance ratings".