If you use Google's Webmaster Tools and have access to a web property, you'll occasionally see mobility error's reported. The most common of these is when content doesn't fit the width of the screen on mobile devices, resulting in the visitor seeing cutoff or incomplete content.
Even if you don't use Webmaster Tools or another web site checking tool, you can see this phenomenon for yourself on your smart phone. Not to pick on Granite Hills (the example is common across many school web sites), the table was probably copied and pasted from an MS Word document which sized the table for print. The fixed width carried over onto the web page and viewers on phones see the right columns truncated with no scroll bar to help them out.
One should only paste for Word with the Word Paste tool:
This is just one type of mobility issue but the most common for sites that have migrated content from an older web site.