A+LS has sound files that read the question and answer text to the student only in basic Math, Reading, Language Usage and Building Vocabulary lessons up to the 3rd grade level. Although there will be a "speaker" icon on the student's lesson toolbar for any lesson in A+LS, only the lessons previously mentioned will actually read the text to the student.
In order to have the text read to students in other lessons, you must rely on 3rd party text-to-speech software. There are many available for download and purchase from the internet, and some even have a free trial version. Most of these operate in the same way: if you can highlight the text on the screen with your mouse cursor, the text-to-speech software will be able to read the text on the screen.
This will allow the majority of A+LS lessons to be read to the student, but there will be some pages where what appears to be text on the screen is actually a picture image (equations from higher math lessons in particular), and the text-to-speech software will not be able to "see" that text to read it.