Subject: Why does reflection of light/sound depend of wavelength?

I am under the impression that electromagnet radiation and sound 
will reflect from an object is its wavelength is small (1/10th?) 
compared to the size of the object. For example high frequency 
sound will bounce off a wall, but low frequency sounds will 
travel through.  Is the cause of this phenomena true for waves in 
general?  Is there a different mechanism for light and sound?  
Does this rule apply to the entire magnetic spectrum? Does size 
refer to "height", "depth", "volume", etc?  I have a 
undergraduate degree in Physics and am currently studying to be a 
science teacher. Thank you for your time.  

Re: Why does reflection of light/sound depend of wavelength?