It is often very hard for a pupil to really know how well they have done in sightreading - especially Associated Board sightreading which tends to be fairly unmusical at the best of times. In my experience examiners are usually quite generous in marking sightreading, especially in the early grades. They have to give 7 if any sort of attempt is made. 12 is a lowish mark and certainly wouldn't be given if things had gone well. Key, pulse and rhythm should all be in evidence (even slightly). Unfortunately examiners' comments don't always reflect the weaknesses. I think some of them try and accentuate the positive in order to make the pupil feel a little better despite the low mark. The same goes for the scales. No examiner would say there was something wrong with a scale is there wasn't. An unknown piano with a different touch can often cause a pupil to play scales rather badly as they can't adjust their touch quickly enough.
It is very disappointing when a pupil doesn't do as well as expected BUT it is worth considering that perhaps your idea of the standard expected might be a little misjudged. I am not saying it is - but when the play the exam game we have to play by their rules. This is why I am not a great fan of music exams per se and prefer to use local festivals and my own pupils concerts to give a pupil goals and incentives. One last thought - if you haven't already done so maybe you could tape your pupils. I find this really helps them listen to their playing in a constructive and realistic way.
If you have the opportunity to attend any sessions run by the AB or Trinity Guildhall you could always quiz them on the standard expected. Some of these sessions demonstrate the kind of playing required and so can be very useful.
hope this is of some help to you. Good luck
