This is very much an asperational goal for MBE. There is no 'average' learner so attempting to design for them is futile. How to personalise? Dinosaur letters has some differentiation on styles of letters. The next generation might identify ones it took more attempts to get right?
We are now moving back to looking at the exam range and plan to take another step towards personalised learning. We are planning to use 3 modes: quiz, play all and personalised where once answered correctly questions are removed and the student is left to work through those they got incorrect. I'm always telling the kids to identify what they don't know. This might help.