PRINCETON — The first time they talked in school about race was in Mr. Campbell's 10th-grade AP U.S. history class. It was the fall of 2014, after a summer when the deaths of Michael Brown in Ferguson, Mo., and Eric Garner in Staten Island, N.Y., had thrust race back into the national spotlight.

Winona Guo and Priya Vulchi, then Princeton High School sophomores, turned to each other at the end of that day, remembering the moment when Tim Campbell, their history teacher, began connecting current events to the history they had begun studying.

"We were having an honest, open conversation about race in class. We remember everybody in the classroom was uncomfortable," Guo said. "Then people started opening up, people started talking about it really courageously."

But in the days afterward, they also heard cold responses and denial as they tried continuing the conversation with friends and classmates. So Guo and Vulchi began interviewing hundreds of people around Princeton, collecting stories on a website they hoped would spark discussion among their peers. The goal, Vulchi said, was "to show that, hey, actual people are going through this, your neighbors, your friends, your teachers. And build that platform of proof but also of empathy."

They soon wanted to do more with the powerful testimonials they had gathered, so they compiled dozens of them into a textbook, now in its second edition and used in 22 states, from Hawaii to Maine.

It's called the Classroom Index because a list of categories at the front tags each story: aesthetic, economic, educational, interpersonal, and more. Some stories are just a few paragraphs, while others run several pages. Two Sikh men from India discuss being confused for Muslim and being profiled at airports; a black woman from Philly tells of the embarrassment she felt when a high school teacher told her she needed only community college because she would never be anything more than a secretary.

"I was too embarrassed to tell my parents. … I actually started to become a little depressed about it," the woman said.

Each story is followed by discussion points, which include statistics for evaluating claims. Cartoons, definitions, and examples connecting stories to recent events are sprinkled throughout.

"Everything that we've been doing is based in this idea that there's this huge need that we've identified in schools across the country" Guo said. "If we all talk about this future of racial justice and solving our problems of race in the future, we have to invest in our schools and institutions now."

Just a few weeks shy of graduating from Princeton High, Vulchi and Guo, both 17, are delaying college a year while they crowd-fund a third version of their book and tour the country collecting more stories.

The book calls on teachers to hold discussions that many would rather avoid, said Campbell, the Princeton social studies teacher whose history class inspired Guo and Vulchi.

"Really, they're putting the onus on us, which is a good thing, to find constructive ways and appropriate ways to provide that atmosphere of safety and openness," Campbell said, "to talk about race in the United States and the world around them."

Princeton is known, of course, for the renowned university that shares a name with the town, which has just under 30,000 residents. The Census Bureau puts median household income at nearly $115,000, more than 50 percent higher than the county and state median. The town is also whiter than the county and state surrounding it.

But race has been hard to ignore, and tensions have flared several times in recent years, including when a student published photos of a "Jews vs. Nazis"-themed drinking game last year.

Vulchi's parents are immigrants from India; Guo's are immigrants from China. Both students said the work is deeply personal for them, and they've felt a stigma surrounding issues of race — walls that go up when they try to talk about it.

The first, 50-page edition of their book was piloted last spring in fifth-grade classrooms in the Princeton public schools. "And then we got right to work on the next one," Vulchi said.

They built an advisory board that includes a professor and the chair of Princeton University's Department of African American studies, and last May were among the recipients of the Princeton Prize in Race Relations. Over the summer, they put together the second edition, more than four times the length of the first.

The department helped fund an initial print run of 500 copies, which was available online and bought out by teachers in a few months. A second run of 250 copies is still being distributed.

Still, Guo and Vulchi said, it's not enough. There are more topics to include, especially about the intersection of race and gender, class, sexuality, ability and disability.  That's why they are taking a "gap" year before college — Vulchi from Princeton University and Guo from Harvard — to travel and collect stories from outside the "Princeton bubble."

Their crowd-funding goal is $26,800 to cover their expenses and the book production.

Like earlier versions, the Race Index, as they're calling the new edition, won't be a traditional textbook, read start to finish. It's a supplemental resource for teachers' already-packed curricula. The book makes it easier, Vulchi and Guo said, for teachers to bring race into an existing discussion.

Maureen Nagle and Yulie Lee, middle-school English teachers at the private Moses Brown School in Providence, R.I., said they wanted to bring race into the classroom because they noticed a disconnect.

"We teach the novel To Kill A Mockingbird, and we found that students were leaving that text thinking that the Civil Rights Movement solved all of America's racial-justice issues," Nagle said.

Nagle and Lee, with other teachers, created a racial justice unit that runs all April. Earlier this month, they hosted a video interview with Vulchi and Guo for their seventh-graders.

The teachers have ordered copies of the book and hope other teachers will be similarly prompted to get over their discomfort with the topic.

"If you're uncomfortable talking about it, the natural human response is to stay away," Lee said. "But racial justice, social justice, if you keep distance, change rarely happens."