In this day and age, there does not necessarily need to be one.
Although when I was in junior school in the 70s there seemed to be a general understanding in education that if you could not write it down well enough to be read, then you could not pass an exam.
Hence my academic options felt very limited at that age. I started senior school with handwriting that was illegible and produced at a rate not adequate of be of much use, and with the spelling capability of a 6 year old. Alas while my junior school was relatively enlightened for the age (having got as far as "He is bright, but dyslexic - we can work out how to have him fit in and not cause us too much trouble"), the senior school was more of the traditional opinion "Dyslexia, never heard of it, a few detentions and canings will soon sort that out!" Needless to say we did not see eye to eye on these points, and soon parted company!
Skip forward a couple of years, and eventually at a school that actually understood how to teach people like me, it was a world of difference. They were content to make sure you learnt and understood but realised the "writing it down" problem could be addressed separately as you went along, rather than treating it as a show stopping road block to all progress and learning. So within a couple of years I could, given enough time, write just about legibly enough that being entered for an exam became a possibility (and the school would routinely make full use of the available exam assistance mitigations that were available (extra time, having a scribe, have a paper read to you etc) as appropriate for the needs of the candidate.