They've taught children in Alaska. They've worked with the Intel Corp. to bring their camp to San Jose, Costa Rica. And they won about $7,000 in grants to run a weeklong camp for middle-school girls at Drexel University.
The Tippermans are just 17.
"This is so far beyond what I would expect from somebody their age," said Jeffrey Popyack, a computer-science associate professor at Drexel. "They want to teach the whole world, I'm pretty sure."
The sisters, seniors at the all-girl Baldwin School in Bryn Mawr, hope to do what they can to show kids, especially girls, what's possible. Less than 25 percent of students in science, technology, engineering, and mathematics programs at middle and high schools and colleges were female in 2010, according to a 2012 federal report.
Teachers, foundations, and countries worldwide are looking for ways to increase the number of girls in these fields. The Girl Rising movement, which advocates for girls' education worldwide, has inspired the sisters.
The Tippermans focus on helping to start robotics programs using five robot kits on loan from Drexel. They have applied for grants to buy more.
To pay for their travel expenses, they babysit, do odd jobs, and sell old clothes. Friends, family members, and students have donated money.
Parents of kids they teach sometimes assume their father is the instructor. Richard Tipperman, an eye doctor, said his daughters know much more about robotics than what he's picked up. He's their assistant in class, but he's mainly the chauffeur and heavy lifter, the girls said, laughing.
The sisters are helping a high school senior in Colorado start her own robotics education program and hope to get more high school students throughout the country involved. They see their youth as an asset that makes them less intimidating to kids.
"This isn't someone who has a Ph.D.," Rachael said. "This is someone that's trying to get through precalc."
The girls stumbled into robotics one afternoon in the seventh grade at Baldwin. Hannah spotted a flier for a robotics program.
"I could have gone the rest of my life not realizing I really like programming," Hannah said.
Last year, they contacted Francisco Burgos, the head of the Monteverde Friends School in Costa Rica, to pitch their robotics curriculum. The girls ran a weeklong camp in June at the school, which stands in the middle of a fog forest and teaches 120 children.
Burgos had been looking for opportunities in technology for his students. He said the sisters were an inspiration to the 25 camp participants, especially the seven girls.
"You could see that something was happening in that classroom," Burgos said. "Hannah and Rachael planted a seed in my kids."
Burgos said he plans to discuss how his school can develop a robotics extracurricular class or its own robotics camp.
While they were in Costa Rica, the girls also partnered with Intel to teach 60 middle schoolers in San Jose.
In June 2013, the girls were in Homer, Alaska, teaching at their first camp. They said they chose to start there to prove to themselves and everyone else that their nonprofit could succeed.
One in the volley of e-mails they sent to groups in Alaska reached the inbox of Elizabeth Trowbridge, executive director of the Center for Alaskan Coastal Studies.
"Quite frankly, I was wondering if it was for real," Trowbridge said.
The Tippermans were offering to pay their own way to Homer and run their robotics camp at no cost for the community's children. After a series of e-mails, a phone conversation, and visits to the girls' website, Trowbridge was convinced the Tippermans were for real.
On Thursday, the girls flew to Boston to visit colleges before their summer of teaching robotics continues. They have two more classes at the Tredyffrin library, their second annual camp for girls at Drexel in early August - funded in part by the National Center for Women & Information Technology - and two classes at Paoli Library before they start their senior year of high school.
Even with all they have done, they said they still hear the occasional skeptical comment about their skills.
"Some people think because I'm a girl I don't know what I'm talking about," Rachael said. "It's definitely changing, though. And it's exciting to see."