Friday magazine columnist Dr Raj Persaud is a consultant psychiatrist at the Maudsley hospital, London, and author of The Motivated Mind (Bantam Press)
"A lot of marking systems are obscure and cavalier because the whole business of analysing what an assessment system should be and then sticking to it involves a lot of work.
"Assessment that appears arbitrary or unjust is demotivating, and if teachers cannot justify grades, a lot of kids just stop bothering. I used to drive my teachers mad because I would frequently take bits of homework more or less identical to my own and say, 'this is the same as mine, but this pupil has obtained a higher mark'. I wanted teachers to give reasons for their judgments.
"Teachers have to be clear about their assessment criteria and stay with it. Transparency in the assessment process is admirable and motivating but it involves much greater commitment from the teacher.
"Lots of professionals rely on lack of transparency to make things easier for themselves. For example, doctors tend not to make a diagnosis transparent because that is the much tougher option; far easier to cloak their practice in mystery."
How the Mind Works, page 21
Brian Smith, 46, is a self-employed plumber from Sunderland. His son Jack is in Year 5 at Broadway juniors, a local primary school. His daughter Emma, 12, started secondary school this year
"If a kid has put their heart and soul into a piece of work, it's not good enough to write 'very good' and move on to the next one. When kids are investing time in their work they need more than an off-the-cuff remark. If it's good, they need to know why it's good so they can produce the same standard in their next lessons. If it's not good, they need to know why too.
"The only comment I used to get on my work was 'see me', and that was usually about something negative. If a teacher had taken some sort of interest in me and shown me in detail what I was doing right and wrong, I might have received top marks in everything, because I certainly had the capability.
"It also works when children discuss each other's work and how to make it better. My son Jack is a bit of a poet and he seems to respond well when he can discuss with others in his class the way he has used certain words and which other words might work better.
"The teacher then asks pupils to go away and take on board what has been discussed and to improve their poems accordingly. That's a good method.
Children seem to be encouraged by that approach."
Kelvin Omonfomah, 15, is a Year 10 pupil at Kingsdale school and performing arts college in the London borough of Southwark. He is taking six GCSEs, including English, maths and science, and hopes to study psychology after 16 and become a psychologist. He is involved with Youth Act, a citizenship initiative at the school aimed at improving the local community "I like to do well so any comment that tells me where I am now and what I need to do to get a top mark is good for me. Teachers at my school do show me my mistakes, but also show me how I can get better. I know I am working for myself towards a goal so I don't feel let down.
"Some pupils might take it the wrong way if they're told about mistakes, but I just think teachers have to spend more time and talk it through with pupils like that, give them more attention.
"Also, it's good to get them together with others who are doing well so they can talk to them about what they need to do to improve. Pupils learn from other pupils better than they do from the teacher, so a pupil getting good assessments can show them the way forward.
"It doesn't work if the good pupil is held up as an example against them, but if he or she encourages them and shows that they can achieve the same level, then that is very helpful."