People often use Driving While Intoxicated (DWI) and Driving Under the Influence (DUI) interchangeably, and for good reason: there is no consistent name for the offense as it varies from state to state.
In Texas, DUI is used exclusively to prosecute people under the legal drinking age and is a Class C misdemeanor. No person 21 years or older can be arrested for DUI.
However, here's the confusing part: both minors and adults can be charged with DWI, the more serious Class B misdemeanor. The difference relates to the burden of proof.
In a DUI prosecution, the State need only prove that the minor was under the influence of alcohol. Because Texas has a zero tolerance policy, and because a person under 21 has no right to drink alcohol, the smell of alcohol on a minor's breath alone can result in a DUI arrest and prosecution. The State does not have to prove that the minor was impaired. Police officers rarely will conduct the full battery of field sobriety tests on a minor because an admission that the person was drinking or the odor of alcohol are sufficient for the probable cause determination.
Police officers have unbridled discretion to choose whether to charge a minor with the Class C or Class B offense. While nobody enjoys getting a ticket, this is the one occasion where it is much better than being booked into jail for the night.
If a person under 21 is arrested and convicted of DWI, there are additional restrictions on their driving privileges. If the person is on probation, he must install an ignition interlock devise on his car for 1/2 the period of probation or until he turns 21, whichever is sooner.