“My father’s cool,” she said.

Money proved to be the least of their problems. The owner of a building in the busy downtown area of Shar-e Naw, which had an invitingly blank wall on a busy street, refused to let them use it, on the grounds that crowds might gather and attract a suicide bomber. They were turned away from Kabul University, told it would be defacing government property.

In a jittery capital, they heard the security objection a lot. But here they were, a bunch of high schoolers, comparatively unafraid. What was the adults’ problem? The last suicide bombing, after all, was three weeks earlier; it’s not like they happen every day, and Kabul is a city of five million.

Finally, way out on Darulaman Road, the principal of Habibia High School allowed them to use a patch of the compound wall around his institution, a public school but an elite one, where President Ashraf Ghani once studied. They painted their wall salmon, with blue inscriptions, including one, “Humanity is my dream,” a famous line by the poet Afghans know as Maulana, but the rest of the world knows as Rumi. He was a 13th-century Persian, but he was born in Balkh, in what is now Afghanistan.

The high school principal, Sayed Shah Bakabuli, was not entirely persuaded. “I gave them my permission because I know it is for a good cause, but I still have my concerns that, God forbid, it should be taken advantage of by the bad guys,” he said.

The youths had other problems. After they pounded their nails in, they returned the next morning to find that someone had stolen them all.

“I guess they needed nails,” Abdul said, but quickly recovered his composure. “It’s O.K. We have more.”