OK this is one of my all-time favorite movies.  I think I just like the characters more than anything.  Released in 1998 this one is definitely an 8 out of 10.  Great intertainment.

Students suspect that their teachers are aliens after bizarre occurances.

What a plot.  Very reminiscent of the Body Snatchers or the Puppet Masters etc. they even make mention of this in the movie which is kind of kitschy.  Anyway the cast (informborrowed from imdb.com is great) :