Your Dashboard (Calendar, Blog, Photo Gallery) are filtered to show you the information that is most relevant to you.
The content is filtered by the classes or groups that your family is assigned to (The classes your children are in) as well as content that is relevant to the whole school.
By default, you will not see information that was meant for other classes, grades, or groups -- this is by design, to keep the "noise" level down. However, if you are interested in what other classes or groups are doing, you can always add them to your filter. The filter can be found either on the Calendar or My Class page.