Issue
Context changes - Clicking the Add an activity or resource link does not announce to screen readers that a modal has been opened.
Guidance - Modal window is not being announced at all to screen reader users.

Standard Level
WCAG 2 3.3.2 (A) http://www.w3.org/WAI/WCAG20/quickref/#qr-minimize-error-cues
WCAG 2 4.1.2 (A) http://www.w3.org/WAI/WCAG20/quickref/#qr-ensure-compat-rsv

Impact
Serious
Critical

Example Link
http://demo.moodle.net/course/view.php?id=625&notifyeditingon=1

Test Steps

1. Login as a teacher
2. Navigate to a course
3. Click the add an activity or resource link with a screen reader on
4. Notice that nothing tells you that the modal appeared.