I wouldn't overly concern yourself with predictions / targets. Whilst no expert, they seem to sometimes be based on the historical data of previous attainment by students - and I don't mean your child
but 'students' who have gone through the whole process and come out the other side with x,y and z.
E.g. If your child attains a level ? in Y6 sats then historically x percentage of these
students go on to attain a B or above in GCSE etc.
As I say, it's one example I've read about and probably quite complicated but has a certain degree of accuracy - obviously!
There are many
factors that decide a students final GCSE grade. I would focus, as a parent, on those [factors] that you and your child are responsible for - and leave the 'statistics' to the school!