LACK OF SCIENTIFIC EVIDENCE
There is a good reason universities do not bother teaching the ideas of Dianetics: because they are not valid. At the center of Dianetics lies a mix of outdated psychological theories, unproven ideas, and wild speculation masquerading as fact. Here we take a quick overview of failure of Dianetics to establish itself in the realm of science.
professionals caution about dianetics
(Credit: Public domain photo)
In 1950, the former president of the American Psychiatric Association also issued a statement condemning Dianetics that stated "It can potentially do a great deal of harm. It is obvious that [Hubbard] has oversimplified the human personality, both as to its structure and function. ... He has made inordinate and very exaggerated claims in his results." 
The warnings quickly made their way to mainstream media like The Nation  and TIME Magazine. 
SCIENTIFIC STUDIES COME UP EMPTY
hubbard goes crazy in response
(Fair Use: New Year's Eve 2006 celebration)
testimonials don't hold water
The first problem is that every type of bogus "snake oil" product -- including junk like crystal healing, numerology, or whatever -- can offer up these types of fuzzy, feel-good stories. The mere production of testimonials, in itself, is insufficient to establish that something actually works. It simply means that some people believe it does. Dianetics is sorely lacking in the proper, independent, scientific studies that would set it apart from other testimonial-laden quackery.
The second problem is that the testimonial has become hard-wired into the process of Dianetics and Scientology in an unhealthy way. Long-term practice includes making students attest to the successful results as a prerequisite for course completions. These mandatory declarations of success take on many different forms. Some are simply eye-rolling quickies, and others are essentially coerced endorsements. This group affirmation is done on a continual basis, and things like exuberant speeches at weekly graduations are commonplace. As ex-members frequently describe, much of this pomp is exaggerated or even completely empty.
the quackery of the "e-meter"
Scientology. (Credit: Wikimedia Commons)
dianetics remains unproven
 "Medicine: Tests & Poison." TIME 18 Sept. 1950. Print. http://www.time.com/time/magazine/article/0,9171,813284,00.html
 Fischer, Harvey Jay. Dianetic Therapy: An Experimental Evaluation. A Statistical Analysis of the Effect of Dianetic Therapy as Measured by Group Tests of Intelligence, Mathematics and Personality. Thesis. New York University, 1953. Web. http://home.snafu.de/tilman/krasel/dianetics_test2.html
 Fox, J., A.E. Davis, and B. Lebovits. "An Experimental Investigation of Hubbard's Engram Hypothesis (Dianetics)." Psychological Newsletter 10 (1959): 131-34. Print. http://www.scribd.com/doc/84889855/An-Experimental-Investigation-of-Hubbard-s-Engram-Hypothesis-Dianetics
 Interview. In Tense Moment, Cruise Calls Lauer ‘glib’. The Today Show. Web. http://today.msnbc.msn.com/id/8344309/ns/today-entertainment/t/tense-moment-cruise-calls-lauer-glib/
 Beecher, W. and Willingham, C. Boiled Engrams – An Elegy to Dianetics. American Mercury August 1951. http://www.scribd.com/doc/124540120/Boiled-Engrams-An-Elegy-to-Dianetics-Beecher-Willingham
 Hubbard, L. Ron. Understanding the E-Meter. Bridge Publications, 1982. Page 50. Web excerpt. http://www.cs.cmu.edu/~dst/E-Meter/faq-on-emeters.html