But if you ask them, they'll tell you she's teaching them much more.
"She really wants for us to have healthier options," said Jasmine Hall of Nicetown. "She's really big on recycling, and taking care of our environment."
Ms. Mac, as her students call her, spearheaded a school-wide recycling drive at Saul.
And she's been instrumental in developing a community-supported agriculture program with the Weaver's Way Co-Op. It's called "Henry Got Crops".
Students grow food for sale and also for the school cafeteria.
"We actually grow fresh lettuce, fresh mix and when I taste it, it's so much better than if you get from the store," said Isaiah Nelson from West Oak Lane.
Jessica's dream is that one day all schools will have programs like this, that put fresh produce on cafeteria tables.
"We would like to see the food produced here at 'Henry Got Crops' go directly back to the cafeteria and for it to be self-supporting," she said, "and for the kids to grow what they're eating. It's a huge, pie-in-the-sky goal, but maybe with some funding and some more great kids, we can have that happen."
Jessica's ideas have already attracted some very high-level attention. She was just named a "Champion of Change" and invited to visit the White House.
Jessica is heading down to Washington on Tuesday. And she's going to take lots of pictures and video of her big trip to share with her students.