Field sobriety tests ("FST's) are typically physical and mental performance tests administered by an officer investigating DUI cases in order to lay the foundation ("probable cause") for an arrest. Officially, your succesful completion of these tests should lead to your release from investigative custody -- but don't hold your breath. Though ostensibly "objective" assessments of alcohol-caused impairment, an officer's evaluation of your perfomance is essentially subjective (exhaustion, nervousness, fear, inclement weather and rough testing environments have been known to look just like alcohol or drug "impairment" -- and vice versa -- so how "dispositive" can they be?). Walk-and-turn, one leg stand, finger to nose and thumb to fingers tests "measure" for affected coordination and balance.  Number counting and aphabet recitation "assess" mental ability.  The officer's conclusion you "failed" any number of these tests will be the basis -- and justification -- for your DUI arrest and the subsequent requirement you be "chemically tested" (blood or breath) to "objectively" confirm the impairment suggested by the FST's.

DUI courts in California are concerned with two Vehicle Code violations:  impairment ("driving under the influence," CVC 23152(a)), which is usually established by FST performance, and statutory blood alcohol level threshold ("driving with a blood alcohol level at or above .08%," CVC 23152(b).  DMV administrative hearings rarely concern themselves with FST's and "impairment" as these hearings are exclusively governed by CVC 23152(b):  convincing evidence the "Licensee" was below .08% and any failed FST performance will be considered irrelevant and the DMV action set aside. 

An experienced and creative DUI attorney can contest and prospectively discredit the officer's assessment of your FST's, often by turning a prosecutor's or jury's attention to the incremental ways a driver may have in fact cumulatively passed the myriad, individual elements that actually make up each kind of test (looking at the trees, rather than the forest, so to speak). But in some ways the "real"  -- the most dangerous -- and the most helpful -- FST is not the ones approved by the National Highway Traffic Safety Administration, but the one hidden in the average police report in the section, "Objective Signs."  The category "Demeanor" holds a field-gathered officer assessment that can make or break you with a prosecutor as much or more so as any formal field sobriety test:  described as "resistant," "combative," or "belligerent" and your FST's can be those of trained gymnast and you'll still be busted with the cop and DA. "Calm" and "cooperative" is the first clue to a prosecutor that a settlement might be had, that generosity might be in order. That the typical "Big Bazooka DUI"- type saber rattling and trial mongering can be avoided. Because your respectfulness from the start, as expressed in your courtesy to the cop, indicates a citizen who, whether he was actually DUI this time, is unlike to repeat the offense in the future. The "attitude test," -- and passing it -- just may be the most important field sobriety test you take, in the field, and at the courtroom.