News about sexual assault in fall 2016 left then-12-year-old Maeve Sanford-Kelly disheartened. She was appalled by the crimes of Bill Cosby and Brock Turner, and how their victims were treated.

But, even at age 12, she wasn't surprised.

"My whole world and my whole life has been: This is what happens. This is how power dynamics play out," said Sanford-Kelly, a Bethesda, Maryland, resident who's now 14.

The middle-schooler considered what she could do to prevent sexual assault and landed on the concept of sexual consent education. She started locally, with help from her friends and her mother, Del. Ariana Kelly, who represents a portion of Montgomery County. Eventually, their efforts had a greater impact.

Maryland is now one of the 10 states, plus D.C., that requires public schools to include information on sexual consent in their sex ed curriculum.

This is the story of how a teen girl and her middle school friends changed sex ed lessons for students statewide.

[NATL-DC] How Lessons on Sexual Consent Are Being Taught to Students of All Ages

As of fall 2018, Maryland students in seventh grade and 10th grade are taught what consent is, how to respect others' boundaries and how to respect one's own.

Sanford-Kelly testified that this is crucial.

“Before we are taught about pregnancy prevention and STDs, we have to be taught about consent,” she said before the Montgomery County Delegation.

Maryland law defines consent as "the unambiguous and voluntary agreement between all participants in each physical act within the course of interpersonal relationships."

Sanford-Kelly said her teachers at North Bethesda Middle School used an analogy about offering someone tea to teach about consent. Someone might want tea on Monday but not on Tuesday. They might want tea with honey but not sugar. Just as you wouldn't force someone to drink a cup of tea if they didn't want to, you wouldn't force them to have sex, the teen said she was taught.

The lessons were "really accessible" and "stick in your mind," Sanford-Kelly said.

She, her mother and her friends first wrote a bill about consent education and took it to the Montgomery County Delegation in December 2016. Sanford-Kelly and her friends testified for the passage of the bill.

After the teens presented the idea at the local level, they decided to think bigger.

"I really felt empowered by the process," Sanford-Kelly said.

The group rewrote and expanded the bill and introduced it before the Maryland House of Delegates.

The bill later died in the State Senate because of a lack of support by Republicans and conservative Democrats.

"I was crushed," Kelly said. "But Maeve said, 'We are coming back next year.'"

Despite the failed statewide attempt, Montgomery County and Baltimore City schools voluntarily implemented the bill in 2017.

When the #MeToo movement took hold in fall 2017, Kelly and the teens gained a second wave of support at the state level. In early 2018, their bill was approved in the House of Delegates and State Senate. Then, Gov. Larry Hogan signed consent education into law in May 2018.

Kelly said she hopes Maryland will set a precedent for other states to follow.

Maryland students learn about consent as middle schoolers and high schoolers. Some educators say the concepts should be introduced even earlier.

Irene van der Zande is the executive director and founder of Kidpower, a nonprofit that works with educators to teach personal safety to students of all ages. The group has collaborated with schools in several states and designed curricula to teach and reinforce skills for students to carry with them long after they leave the classroom.

Van der Zande urged schools to teach students about consent repeatedly.

“Raising awareness does not create competence,” she said. “Practice is key.”

Sanford-Kelly said she thinks her efforts have already had an impact. Her classmates seemed to understand the allegations against Supreme Court Justice Brett Kavanaugh during his nomination hearing.

"They were really able to take it in and register it," she said.

Sanford-Kelly said she and her friends saw that they could create change, despite their youth.

"It made me look forward to the future. I'm excited for what it means for students and what it means for society," she said.