Once the Chrome extension has been added, within your Google Documents a toolbar is accessible that provides text-to-speech (so, for any document provided to students by the teacher, or as an editing tool), text prediction, picture and text dictionaries, highlighting and more. For SLPs, I especially like the vocabulary tool that will collect highlighted vocabulary words within a document and add them to a new document with definitions and pictures for each word.
Within intervention sessions, Read and Write would be useful for its web research component- the toolbar is also accessible on webpages so they can be read aloud and highlighted, as well as reviewing and highlighting documents, teaching editing skills, and the above mentioned vocabulary feature. For students who would benefit from long-term access from all the above tools, after 30 days a subscription ($99 annually) is required but the text-to-speech feature remains free. Educators, after adding the toolbar to their own Google account/Chrome browser, can apply for a free premium teacher subscription.
I have produced a tutorial handout for installing and using Read and Write for Google that you can find at this link.