As her second-grade students take out their lunches, teacher Leticia Moreno quickly spots two with forbidden food - a burrito and quesadilla made with white flour tortillas.
"I will get them peanut butter and honey on whole wheat," Moreno says, taking away the offending meals.
Moreno is a teacher at the Children's Success Academy, a 10-year-old charter school on Tucson's south side for children in kindergarten through the fifth grade. The school is unique for its food rules - it bans not only white flour, but refined sugar and anything it defines as processed food.
"It has to say 100 percent juice. If it just says 'natural,' that's not allowed," 8-year-old third-grader Jacob Price says as he bites into an apple. "I wish we could bring more kinds of food. I like Oreos."
But Oreos will never blight the Children's Success Academy as long as school director and founder Nanci Aiken is in charge.
Aiken, a scientist who holds a doctorate in cell physiology and once worked as a cancer researcher at the Arizona Cancer Center and Johns Hopkins Medical School, is an unabashed food cop.
"I feel like the Wicked Witch of the West a lot of times, but it makes such a big difference," says Aiken, who is also president of the governing board for Tucson's El Rio Community Health Center - Arizona's oldest and largest community health center.
"When you eat sugar, especially by itself like a candy bar, you get a rush and crash. An apple will not give you instant gratification or a rush, but it lasts longer," Aiken says. "An apple and a piece of cheese is ideal - your blood sugar will go up gradually and then will go down gradually over a period of hours."
The rules seem drastic to many parents sending their children to the school for the first time. Since the school has no cafeteria, all students must bring their own lunch.
"It is challenging mainly because in grocery stores it's so hard to find anything without sugar. When you look at the label, so many things aren't allowed," says Breanna Chacon, 30, who has two children at the school.
"It really does make a difference. It balances them out," says teaching assistant Isabelle Medeiros as she confiscates a student's packaged Ritz crackers and cheese spread. "I will send this home with a note, explaining why it isn't allowed."
The school's emergency food supply of "yes" foods like peanut butter and honey is provided through donations and fundraisers.
Among the "no" foods: flavored yogurt, canned fruit, American cheese, processed meats, white bread, peanut butter made with sugar, and virtually all packaged crackers except Triscuits, because they are baked with whole grain.
Not everyone supports such extreme food rules - especially if they extend to the home.
"There are all kinds of emotional and behavioral problems that can happen if you tell a child to never, ever eat a cookie. They may do just the opposite once they are at a rebellious stage," says registered dietitian Nancy Rogers, coordinator of the Worksite Wellness Program for the University of Arizona's UA Life & Work Connections.
"Food is in such abundance here. It's not like living on an island where you are never going to see an Oreo. You want to train kids to make good choices to keep their bodies healthy."
Rogers recommends moderation. Sugar is not bad in small amounts, she notes. It's a carbohydrate that is burned for energy.
"The studies don't substantiate that additives or preservatives would cause behavioral problems in children. However, there is anecdotal evidence," Rogers says of Aiken's approach. "If the parents are wanting to try it, there's no harm in that."
Aiken does not relent. Not for Halloween nor Valentine's Day. Not even birthdays.
"I always say no. It makes them think and be more creative," Aiken says. "You don't need a cake. They can have nuts, or fruit."
If all U.S. families followed her school's food rules, Aiken believes, childhood obesity would be a rare problem.
"There is also the physical activity aspect to consider," she says. "However, it is much more difficult to become obese by overeating fruits and veggies."
Preventing obesity is only one reason behind Aiken's rules. Overall health is the key factor - particularly for children who, like many of her students, have behavior problems.
“A lot of kids who are challenged and diagnosed as having attention deficit disorder biochemically maybe are more sensitive to sugar — it’s possible they metabolize it differently,” Aiken said.
“The kids with ‘behavior problems’ are usually very bright. I’m not a fan of medications for behavior. Only one to two percent of kids on them really need them.”
Andreina Barrios, 6, often brings plain unflavored Fritos corn chips, which are a "yes" food because it's a whole-grain food. One recent lunch included scrambled eggs wrapped in a whole-wheat tortilla, as well as water and tomato juice.
Her classmate, 5-year-old Luz Michel, brought whole-wheat noodles, plain chips, juice and sliced peaches.
"We are what we eat. It's true," Aiken says. "If you buy a new car you aren't going to put sand in the gas tank. Why would you want to do that to your body?"