"Can I go to the bathroom, Mr. Substitute?"

I looked at the high school sophomore who'd just spent 30 minutes giggling with her neighbor, applying make-up and ignoring the Spanish worksheet on her desk.

"No," I said. "Wait until after class."

"But that's 20 minutes!" exclaimed the 15-year-old.

"Your teacher said no bathroom passes," I explained.

"I'm so sure!" she cried.

California has two main requirements for substitute teachers in public schools. First, one has to pass the California Basic Education Skills Test, which checks basic math, reading and writing skills.

Second, you need a bachelor's degree. That's important because otherwise we might have 18-year-olds running classes of their former schoolmates the first September after they graduate. The CBEST is nothing compared to the SAT and would pose no challenge to good high school students.

But colleges don't teach, and the CBEST doesn't test the finer points of substitute teaching that make the job bearable and even fun. I compiled the following list during my time this year at Lincoln, Lowell and South San Francisco high schools and in East Bay districts like Hayward and San Lorenzo:

Rule #1: Keep 'em busy.

For high schoolers, that means the assignment is due today, whether it's possible to finish or not. If they need more time, push back the deadline at the end of class.

Hayward Unified School District's "sub" manual suggests having primary kids alphabetize their spelling words or "think of animals that live on a farm, in a jungle or underwater." Personally, I've found there's nothing like a game of "Duck Duck Goose" or a rousing chorus of "The Wheels on the Bus" to run out the clock until recess.

Rule #2: Keep the upper hand.

Don't let a kid take roll. Keep the kids in their regular seats. Never leave the room. Be positive, but kick a few out if they ask for it; the principal can handle them and the rest will shape up.

Make sure the kids stay on task, whether you understand the task or not. Teaching Spanish, which I've studied only at the Taco Bell drive-through, worried me at first. But I was surprised how far I got with "Read the instructions" and "Look it up in your book."

Other tips: "tight" is the 90s synonym to "cool" and "hip;" know how to run a VCR; and stifle all student attempts to start a game of "20 Questions" concerning your personal life!

Bathroom policy is a subject unto itself. "One at a time," the first rule, was easy. How to look into a teenagers' eyes and tell whether the kid's bladder is full is a trick that took longer to learn.

"I can't hold it," the girl insisted.

I decided to give her the acid test.

I pulled the U-shaped bathroom pass out from the podium for the girl. She gaped as if I'd asked her to eat a bag lunch or appear with her parents in public.

No teenager who doesn't really have to pee will carry a discolored toilet seat down the hall.

"I'll wait," she said, rolling her eyes. "Whatever!"