In order for Speech to Text to work in the exam room, you must make sure you computer is set up properly. First, click on the Apple logo in the upper left corner of your screen, then click System Preferences.
This will open up the System Preferences menu, and in the second row to the right will be Sound. Click on that.
In the Sound menu, click on the Input tab to see the list of microphones available to use. This is where you want to select the mic you'll be using. If you're using a laptop, it will have a built-in Internal Microphone that is usually selected by default.
If you have headphones with a mic attached and they are plugged in, you'll see them listed as an External Microphone. Either of these will work, and you can test them by talking and seeing that the bars in the Input level fill up.