Can you consume alcohol the night before your 21st birthday? (California)?

Back in high school, my gov/econ teacher told us you can drink alcohol the night before you actually turn 21...This makes sense to me, so that people won't drink heavily between 12am-2am.

Since I'm turning 21 in a couple weeks, this information would be really helpful.
NO, that's not true. You have to already be 21 in order to legally purchase and consume alcohol in California.
No you can't. You're not legally 21. You can however consume it between the times of 12:00am and 2:00am.
The 'night' before your 21st birthday is the day you turn 21, so yes you can. Say you turn 21 on July 10. Then you can sit up at night on July 9, and as soon as the clock hits midnight you can drink alcohol.
Just try buying alcohol in a store or a bar or a restaurant before you turn 21. You will have the answer to your question.
Not legally. You are not 21 until Midnight on your birthday. Sorry!

It may be too late to show up your government teacher, but if you can you might give him this information.

The common law rule is that you turn 21 (or any other age) on the day BEFORE your birthday. Early California law was in conflict on whether this was true under California statutory law. (See, for example, Ex parte Wood (1907) 5 Cal.App. 471.) However, the issue was conclusively settled in In re Harris (1993) 5 Cal.4th 813, which held that your age changes on the date of your birthday, not the day before, under section 26 of the Code of Civil Procedure.

Note, however, that legally you turn 21 at midnight, so you could legally drink from midnight until 2 a.m. I think the odds of any bartender serving you at that time are low, however.
No you cannot.

When the clock hits midnight, it's the next day.