For the moment, you might want to consider adding oral assessment/elaboration to his accommodations, since voice-to-text is not efficient yet. Long term, of course, that won't be a sustainable solution (for college and beyond), but it will allow him to develop and demonstrate a bit more of his language expression and knowledge acquisition in the meantime.
Is OT working on handwriting? Or are they also working on keyboarding, which is going to have to be his long-term plan? And if he has articulation issues that are significant enough to interfere with speech-to-text, then does he have speech services? At this age, it's no longer merely developmental.
