I am assuming your students are sitting their exams in English? You will need to check with the exam boards you are using with regards to their requirements for scribes – for GCSE’s they need to have a standardized score of below 84 in an area which would impact on writing e.g. spelling or the DASH to qualify for a scribe – only if English is the students first language. It is important that English is the students first language or they won’t be able to have access to a scribe as this is seen as an unfair advantage. As mentioned before it doesn’t work well for MfL exams due to having to spell out letter for letter words. I would suggest getting students to type for these exams if their handwriting is particularly poor.
I have a really useful template I use to collect evidence from teachers which allowed them to make a comment at the bottom. Inbox me if you need it (@hjteaches). If teachers across multiple subjects highlight they benefit from a scribe and that their way of working is to have work transcribed in lessons you can gather evidence that way. We also ensure that students have two rounds of mock exams before they sit their actual exams and those with scribes have two chances to get used to it in exam conditions prior. Again this helps to build evidence for their normal way of working.
Finally scores from standardized tests should have been completed within 3 years of the exam date to be valid – so you couldn’t use data from prior to Summer 2016 for a student sitting an exam now.
Hope this helps.