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If you want a 'meaningful grade', why not have a single board so that every student is examined in the same way on the same syllabus?
So could you tell us what 'meaningful grade' means in your mind, because as you confirm different students study differing courses!
I'll have a last go at this (God knows why...)
Let's imagine a single board. Oh, wait, in Wales,
there is only one board. Moving on. Now stick to say, Maths. One board, one subject. Even Ellal is still with me at this point, surely. The board has an expert panel and the members (maybe one for pure, one for mechanics, one for stats) set the exam papers for this year's a level. The papers are accepted by the board. The papers are set by reference to the agreed specification, the one agreed by the Welsh Government. A mark scheme is set to allocate the marks, and the markers- maybe 10, 20, 50 people for Maths- have to mark to it.
The papers get marked, and hey ho, the highest raw mark in Wales is 62/120. ****, the paper was too hard! (These results are across Wales, so IT IS NOT one school's lazy teachers to blame, nor is it a poor bunch of students this year) Not to worry, we have. a mechanism
for normalising the grades when this happens; a 'smoother-outer' as it were. It's called a grade boundary, which is not set until the marks are in.
So, your kid did a crippling paper, got an A with 50 marks; mine had a piece of **** paper, got an A, but needed 70.
The 'unfairness' in the papers is taken out.
Now, your idea is what? Same paper every year? Good luck with keeping it secure. Same
standard of difficulty every year? It can't be achieved in the way you describe, hence the grade boundary system. Hence the 'meaningful grade'.