On October 8, 2018 Google announced a new feature that a lot of educators are going to love. Automatic, real-time captioning is now available in Google Slides.
If you are presenting in full-screen and have a microphone connected to your computer, you can enable the captioning feature and Slides will display captions of your speech in real-time on the bottom of your slides. Currently the feature is only available in the Google Chrome web browser and in US_English.
Google noted that captions may not be accurate if you do not speak clearly, have a distinct accent, or there is a lot of ambient noise in the room. Having a microphone (like the ATR-2100, Sampson Q2U, or a decent lapel mic) will make it easier for the computer to pick up your voice and produce those captions.
This will help you to make presentations more accessible to your students. For hearing impaired students the captions help them to follow along in class as your present content; but can be valuable for students with a hearing impairment by making it easier for them to follow along and take notes based on your presentation and your lecture.