(CNN) -

Thousands of freshmen at the University of California-Berkeley swiped their student cards last week at the doors of Zellerbach Hall and filed into the dark auditorium for one of the few mandatory sessions in their three-week welcome program.

Dealing with sexual harassment, alcohol and stress were on the 90-minute "Bear Pact" agenda -- much of what you might expect in a freshman orientation, said 17-year-old Alexandra Yoon-Hendricks, who attended one of three sessions offered.

One topic, however, caught her by surprise: the definition of sexual consent, the way we let others know what we're up for, be it a good-night kiss or the moments leading up to sex.

A slide projected onstage defined consent through three "pillars:" "Knowing exactly what and how much I'm agreeing to; expressing my intent to participate; deciding freely and voluntarily to participate."

Instead of waiting for your partner to say "no," speakers onstage told students, you should seek an explicit "yes." It could come in the form of a smile, a nod or a verbal yes, as long as it's unambiguous, "enthusiastic" and ongoing.

To Yoon-Hendricks, a staff writer for the teen publication Sex, Etc., it was a refreshing stance for a school to endorse.

"I loved hearing that, because I'd never really heard people describe consent in that manner before," she said. "Instead of saying 'no means no,' 'yes means yes' looks at sex as a positive thing."

It's a message students across the country are hearing as they return to campus for a new semester. Often referred to as affirmative consent, it's the concept of both parties agreeing to sexual conduct, either through clear, verbal communication or nonverbal cues or gestures.

"There are lots of ways to express 'yes.' My favorite is 'yes,'" a speaker told the Berkeley freshmen.

California might become the first state to make affirmative consent law. Senate Bill 967 would amend the education code to require schools whose students receive financial aid to uphold an affirmative consent standard in disciplinary hearings and to educate students about the standard. The legislature sent the bill to Gov. Jerry Brown last week.

The legislation has the support of victims' rights groups, violence prevention groups and the University of California System. But critics worry it could define a great deal of sexual activity as "sexual assault" and undermine due process rights of the accused.

Even if Brown vetoes the legislation, consent will still be defined on the University of California's 10 campuses as an "affirmative, unambiguous, and conscious decision by each participant to engage in mutually agreed-upon sexual activity."

What that looks like in practice is harder to explain, leaving institutions grappling with how to make the policy more meaningful than words in a student handbook.

"There's varying language, but the language gets to the core of people having to communicate their affirmation to participate in sexual behavior," said Denice Labertew of the California Coalition Against Sexual Assault. "It requires a fundamental shift in how we think about sexual assault. It's requiring us to say women and men should be mutually agreeing and actively participating in sexual behavior."

A laughing matter?

It's a shift schools have endorsed before with mixed results.

Ohio's Antioch College became a target of national mockery after revising its Sexual Offense Prevention Policy in 1993 to require that students give ongoing verbal consent at each stage of intimacy.

The policy reads today much as it did then: "Consent means verbally asking and verbally giving or denying consent for all levels of sexual behavior."

Consent is required regardless of the parties' relationship, prior sexual history or current activity ("Grinding on the dance floor is not consent for further sexual activity," the policy reads). It cannot be given if the person is intoxicated, unconscious or asleep.

The rule was mocked in a "Saturday Night Live" skit featuring Phil Hartman as the host of the game show "Is It Date Rape?" The "date rape players" acted out encounters that Antioch students (played by Shannen Doherty and Chris Farley) called out as "date rape" or "not date rape."

The "date rape players" talked like "robots," using cold and clinical language, said Louise Smith, Antioch dean of community life. In reality, "good communication between sexual partners can be fun, even sexy," she said.

"If you think about it not in the 'SNL' kind of way, but as a conversation that's ongoing as things progress, it can work," Smith said.

The school, which closed in 2008 and reopened in 2011, has no empirical way of measuring the policy's success, said Smith, an Antioch alum. But the school feels vindicated by SB 967 and renewed dialogue around consent.

"Despite the fact we were ridiculed, we were extremely proud of this policy. We felt like it was forward-thinking and in line with our values about social justice, equality and health."

Meanwhile, affirmative consent continues to be fodder for sitcoms and sketch comedy shows, highlighting the "profound disconnect between the policy's bureaucratic requirements" and the reality of human sexuality, said Joseph Cohn, legislative and policy director for the Foundation for Individual Rights in Education, a legal advocacy group that has come out against the legislation.