When a tooltip or equation is added to a new SC lesson, an accessible file, ada_annotation, is created within the lesson folder for that item. This .html file is what includes the "Description for use with screen reader/assistive tech". As well, for items such as equations, a readable form of the equation is generated automatically and included in this file.
SoftChalk uses JAWS screenreader to test accessibility. JAWS will recognize a Tooltip as a 'link'. It works like any other link and can be activated with 'Enter' (which is the keyboard shortcut for 'mouse click'). This opens the Tooltip dialogue which then gets read. As long as the Tooltip is open it is essentially part of the lesson page.