Youths make a sweet stand

“You’ve got to scream it out,’’ the 8-year-old said to his friends before yelling: “Lemonade! Lemonade!’’

Lemonade stands went up in Roxbury and other neighborhoods all over Boston yesterday, as an estimated 700 children learned lessons about sales and charity while participating in Lemonade Day, a national event that began in 2007.

The goal was to make enough money “so we could give a donation and keep some for ourselves,’’ Sebastian said.

“We learned that it’s, like, really fun to help people out,’’ said 9-year-old Samyia Jordan of Roxbury.

Most stands yesterday were sponsored by agencies, businesses, and foundations. Friends of the Children, a Boston agency that gets mentors to work with students from first grade through high school graduation, coordi nated the Dudley Street stand, where the proprietors chose Dana-Farber Cancer Institute as their charity.

“It was my idea,’’ said 10-year-old Jendayi Williams. “We’re doing it for the cancer people, to give them toys.’’

Babson College was the local organizer for the national event

“We hope to give as many people as possible a taste of entrepreneurship at as early an age as possible,’’ said Leonard Schlesinger, the school’s president, who visited several stands yesterday, including the one in front of Engine 14 and Ladder 4, the Boston Fire Department station known as Fort Dudley.

Since its inception in Houston, Lemonade Day spread by 2010 to 14 cities, with about 66,000 children participating.

Working with adult supervision, the children who staffed stands yesterday in Boston, Newton, and Wellesley figured out how to set up a one-day business and how much they needed to deduct from profits to cover the expense of making the lemonade.

The project, Schlesinger said, “makes some of the basic subjects, like math, relevant.’’

“We also get to have some experience on how to do a lemonade stand,’’ said Yadhirys Beato, 8, of Roxbury.

Selling lemonade, Schlesinger said, provided a lesson in sizing up a target audience. Children running the stand at the intersection of Boylston and Charles streets in the Back Bay quickly learned to approach parents with children because they were the most likely customers, he said.

The crowd at Dudley Street burgeoned with the arrival of Mayor Thomas M. Menino.

“I’m the mayor,’’ he said, shaking Jendayi’s hand. “I’ll have a big glass.’’

“You picked us?’’ she asked upon learning that the mayor chose the Dudley Street stand as his lemonade stop for the day. “That’s so cool.’’

Menino added a math quiz to the mix, first inquiring if the children knew fractions, then asking how much money was one-fourth of a dollar. “Tick, tick, tick, tick,’’ he intoned, head tipping back and forth like a metronome as he waited for an answer. It took a while, but the children answered correctly: 25 cents.

The stand drew a steady stream of customers, most of whom handed a few dollars to the children, who divided the bills between a steel box that held money designated to cover costs and a large tip jar.

“I want to help kids who have cancer and are sick,’’ said 9-year-old Raphiel Feliz of Roxbury, who also was sitting at the lemonade table. All activity at the stand halted a couple of times when the Ladder 4 truck, siren blaring, left for a call.

“I want everybody to be happy in this world,’’ Raphiel said.

Bryan Marquard can be reached at bmarquard@globe.com