Google Voice Typing
Google Voice Typing allows the user to speak and the computer will type the words. Many of your students could benefit from this feature. It would require a headset microphone to work the best and probably a quiet location. The program seemed to work rather well with my voice, is already installed in all Docs, and was easy to use.
Open Google Doc
Go to Tools
Allow use of microphone if necessary
Click in microphone when you want to speak, click to turn off
On a Chromebook, you would only be able to have headphones or microphone plugged in at one time unless you had an adapter. It does work without the adapter. The tech wiki page (https://lowell-schools-technology-wiki.wikispaces.com/Approved+Equipment) has suggestions for headsets and the adapter so you can have both headset and microphone plugged in at same time on Chromebook.