For two hours every evening, six students sit on the floor at the Quba Institute of Arabic and Islamic Studies in West Philadelphia, their backs against a wall, heads buried in workbooks. It may take years, but they're on their way toward a goal that few in the school's three-decade history have reached.

They are attempting to memorize the Quran — all 114 chapters and 6,200 verses, in Arabic, of the sacred text that Muslims believe was revealed to the prophet Muhammad. If they succeed, they will become distinguished members of the Muslim community, respected for their expertise. When they die, they are granted special access to paradise.

"We call them the Keepers of God's Word," said Imam Anas Muhaimin, the institute's director. "It's every parent's dream that their children memorize the Quran."

As young as 9, the Quba students are taking on the holy challenge, a centuries-old tradition, at a time when Islam and its institutions are a burgeoning presence in the region. Worldwide, it is the fastest-growing major religion, with 1.8 billion adherents; Muslims are expected to outnumber Christians by 2075, according to a 2017 study by the Pew Research Center. In the United States, their numbers have risen from 2.75 million in 2011 to nearly 3.5 million.

As many as 400,000 live in Eastern Pennsylvania and Delaware, and 180,000 in New Jersey. Those populations are now served by at least 175 mosques and about 40 Islamic schools, according to the Council on American-Islamic Relations.

Twenty years ago, after-school classes for Quran memorization were difficult to find, said Imam Numaan Cheema, of the Zubaida Foundation, a nonprofit that includes a mosque and school in Yardley, Bucks County. If they wanted their children to learn the book by rote, he said, area families often had to send them away to boarding schools.

That is no longer the case.

Zubaida added a memorization course two years ago. The Iqra Institute in Trooper (Iqra, Arabic for "read," is the first word revealed in the Quran) was founded three years ago, in part to meet a growing demand for Islamic education and Quran memorization, said Abdullah Bakran, director of the Montgomery County school. The GCLEA (Gracious Center of Learning and Enrichment Activities) in Cherry Hill began a Quran memorization program in August.

Increasingly, Cheema said, young Muslims seeking instruction are being influenced by the extensive coverage of the faith on television and in social media. They want to learn more.

Only about one-third of those who attempt the feat succeed, typically taking three to five years. They earn the title of Hafiz, and are called on to lead daily prayers, as well as special supplications during the holy month of Ramadan. Many go on to become imams.

The tradition of memorizing the Quran dates to the revelation of the holy book itself, said to have spanned 23 years starting in 609. The text was preserved in writing by scribes and memorized by Muhammad's companions after his death. Generation after generation learned the tenets of the faith by heart — an oral tradition that serves as a kind of eternal fact-check, Muhaimin said. "It's difficult for someone to change something in writing because so many have it memorized."

Though students are mostly younger, some are adults, and increasing numbers are women, who in the past were discouraged from seeking study outside the home in some countries, Cheema said.

At the Quba Institute, Chevonne Byas, 31, and her 9-year-old daughter, Nuriyah Byas-Harper, have been taking classes together since last fall. They meet with Muhaimin for about two hours in the evenings in the narrow mosque adjacent to offices and classrooms. Students memorize at their own pace. When they have questions, they approach the imam, who is seated at a floor desk. When they are finished, they return to their places against the wall.

"It gives me a sense of accomplishment," said Byas, a science teacher. "I've invested so much time and study in secular things — my education, my degrees. [I asked myself,] 'How much time have I invested in my spiritual growth?' "

So far, Byas has memorized a portion of a juz, one of the 30 parts into which the Quran is often divided. Nuriyah is just beginning to memorize. "She pushes me," Byas said of her daughter's enthusiasm.

Memorization instruction is often independent study, with goals set for memorization weekly, monthly, annually, Cheema said. Before instruction starts, students are taught to read Arabic. Then they are given a few lines, or pages, depending on their aptitude. With each new assignment comes a recitation of previously memorized texts to help with retention.

Students also must learn tajweed, a set of rules for the pronunciation of words when reciting the Quran.

Iqbal Zaman started to memorize the Quran as a 14-year-old in Pakistan. He didn't finish. His studies were interrupted by college and a career. Now 47 and a resident of Phoenixville, he is in a class at the Iqra Institute, alongside his 13-year-old son, Ma'az.

"It was like a mission I never accomplished," Zaman said. "I'm settled now, so why not finish what I started?"

For Ma'az, it's "not that hard," Zaman said. For his father, it's a "constant struggle" that becomes more difficult as you memorize more of the holy book. The challenge of retention is conquered by daily recitation.

"When I started, it was grueling," said Imam Rashid Ahmadi, 34, of GCLEA. "It's like weightlifting. You want to gain muscle. It's painful, but after a couple years, you see those muscles, and it makes it all worth it."

Since the Quba Institute began teaching memorization in 1988, six students have successfully memorized the Quran out of the hundreds who have begun the program. The last to graduate was in 2010. In the African American community, in which many are converts to the faith, memorization is not a longstanding tradition, Muhaimin said.

African American Muslims, consequently, often rely on a Hafiz from immigrant Islamic communities to recite the Quran for prayer and on holy days, Muhaiman said. "But that time has passed. We have a responsibility to empower ourselves, to better represent ourselves in our faith."

Abdullah Patterson, 13, of West Philadelphia, has learned seven of the 30 juz by heart. He wants to be an imam, and has been memorizing the Quran after school with Muhaimin for five years. He loves to watch football and play video games. But outside interests don't outstrip his desire to finish what he started.

"When you learn it, you get a big reward — paradise. There are gardens, rivers flowing, things you can't imagine," Patterson said. "I know I will finish."