It seems there is evidence that teachers may be biased in their teacher assessments, and that children are "stereotyped by 7".
Here's a link to the full paper, along with a link to a summary.
The suggestion here is that teacher assessments might be less accurate than, for example, externally examined tests or child completed tests and that teacher bias may be at least partly responsible for the disparities found in achievement between girls v boys and also for pupils needing FSM or having SEN compared to other pupils.
I've just settled down to read the full paper but would like to know what parents and teachers think - does this research match your experiences / make sense to you and if so what would you do about it?