Poltergeist

A poltergeist (German for "noisy ghost"), when not taking time out of its busy schedule to make TV shows and movies, spends most of its time lurking in castles, ruins, old Southern plantations, attics, and basements. Anywhere people like a good story, some scary noises, and the odd wind rustle or two.

Poltergeists are very shy, so sadly, they have been reluctant to come out and play with scientists when they are visited by lab-coated intellectuals. Nevertheless, they do exist. Just ask anyone who makes money giving tours through old war fields, slave ships and abandoned or disturbed graveyards. Tour guides will assure you that the breeze you feel coming from the dank depths of a 10 foot deep hole has nothing to do with atmospheric homeostasis, but with the disturbed or evil thoughts of the dead, near dead, and tragically murdered.

Evidence of poltergeist activity
All of these descriptions come from people on the web or on sites that detail what standard poltergeist activity looks like.
 * Noises, generally at night (totally not the wind, or animals, or the house settling)
 * Changes in temperature (can't possibly be natural breezes)
 * Illogical fear or panic in the mind of a logical person, when nothing happened to cause it (none of us has experienced that!)
 * Static or "foggy" images in pictures taken by auto-focus cameras (which never mess up, don'cha'no)
 * Hissing or crackling noises in the background of otherwise straightforward home videos (all cameras always hyper accurately record footage and sound)
 * The "feeling" of being watched or touched. (none of this has ever been observed in clinical settings, no)
 * Unusual or unexplained smells (obviously, we know every single smell and where they come from)
 * Children's toys being 'out of place' or broken ('cause we all know our child would never break his or her toy).

Less standard example:
 * An old transistor radio assumed to be broken unexpectedly coming to life.

Cause
According to scientific-sounding paranormal experts, poltergeists are caused by "an abnormal amount of energy built up" at a location: "Such energy build up can be released from active, hormonal preteens/teenagers. Typically, young physically active girls, age 12 to their 20's are believed to create this culprit of strange paranormal, poltergeist like, activity. However, preteen/teen boys can also give off energy in the atmosphere."

Considering how many emotionally/hormonally-charged adolescent and teen boys and girls are gathered in secondary schools and universities all over the world on a daily basis, it's amazing that poltergeists allow any scholastic work to get done at all.