The spelling is unfortunate, but, your DS won't be the only dyslexic teen taking the exams, so, hopefully, the examiners will be more able to decipher the meaning that you or I are, when accustomed to marking work with poor spelling.
DS types for everything, except maths and French. The SENCO said that there isn't anyway to type in French. I know that you just change the keyboard settings and memorise where the changed keys are, because I've had to do it for another language in a business setting. However, I didn't contradict her, and now, a few years further on, the upshot is DS is having to handwrite in French.
I really struggle to read DS's writing. Its not illegible its more like every word in every sentence follows the sequence: legible, legible, barely-legible, legible, guess, no-idea, legible, barely legible. i don't know how the teachers/ examiners can make it out.