After spending nearly half his life at an Achievement First charter school in Brooklyn, Marquis Wilson was prepared to write college essays and was diligent about showing up to class at SUNY Purchase.

But Wilson, now a theater major headed into his junior year, felt less prepared to make basic choices about how to spend his time once he got to college.

“I found myself at a Nerf club on Wednesday nights,” said Wilson, one of 31 who graduated from Achievement First Brooklyn High School, in Crown Heights, in 2013 as part of its inaugural class. “I wanted to try everything because I didn’t get to be free in high school.”

“My schedule was pre-determined,”he added, “whereas in college it’s like you can do this, and this, and this, and this.”

Wilson and two of his classmates reunited earlier this month at the request of the network’s board. Its members, led by board chair and former Brooklyn College dean Deborah Shanley, had two essential questions: “Did we prepare you? Where did we fall short?”

Charter school network leaders in New York City and across the country are looking for answers to those questions as they increasingly serve older students. Charter high school graduates have tripled in New York state since 2010, from 600 to 1,800 last year. Most of those students are black or Hispanic and from low-income families, groups that obtain four-year college degrees at less than half the rate of the national average.

And as charter schools try to push more students toward college graduation, they’re confronting fundamental questions.

How do they tweak their models, which include longer school days, prescriptive teaching practices, and strict discipline, to work best for older students? Is their singular focus on graduating from college right for every student? And how can they learn from the first students who have gone through their high schools into college?

The candid discussion at Achievement First’s board meeting was aimed at helping its schools answer the last question.

Wilson was joined by RoBrean Black, a forensic psychology major at John Jay College of Criminal Justice, and Avril Gordon, who is studying public health at Franklin and Marshall College. Their academic preparation was mostly solid, they agreed, though Gordon wished she’d had access to a more advanced science curriculum.

Other parts of the college transition, like choosing courses and navigating the glut of extracurriculars, felt like a shock after a high school governed by strict behavior rules and class procedures, they said.

Black recalled being sent to a detention room instead of class for a school day because the soles of her shoes weren’t the right color. Wilson said he racked up behavior demerits because he often wasn’t seated as the class bell rang.

“Some of the rules of Achievement First were a little too extreme sometimes,” Wilson said.

“There was a little too much handholding,” Gordon said, recalling the frequency with which her teachers checked to make sure students were completing their work and understanding concepts.

Robert Schwartz, a professor at the Harvard Graduate School of Education, said questions about how charter schools adapt their models to work for high school students are emerging nationally. The tension, he said, is that their practices “seem to work very well at raising test scores in the early grades.”

“But if you don’t at some point in that progression really shift in that strategy to enable kids to take more responsibility for their own learning that’s less teacher-directed,” he said, “the transition to higher education can really be very bumpy.”

Jeffrey Litt, the longtime superintendent of the high-performing Icahn Charter School network, said he didn’t want to expand to high school because he didn’t think he would be able to compete with the city’s top schools and because he worried about pulling off that complicated transition.

“If we keep a kid in that environment through twelfth grade, the child now leaves us and heads to college and they don’t know any other world,” he said. “They’re going to be shocked.”

Achievement First’s level of attention to student behavior is a hallmark of many charter school networks, as is the expectation that all students will go to college. Hallways decorated with college pennants and classrooms named after teachers’ alma maters are the norm. Even in the earliest grades, classes of students are referred to by the year of their anticipated college graduation.

The high school’s approach didn’t work for all students. The state says its four-year graduation rate for 2013 was 84 percent, but that doesn’t account for the students who transferred out of the school. Achievement First’s first class saw high attrition over its four years, shrinking from 62 to 38 students.

Spokeswoman Amanda Pinto said some students were held back, and Black said other classmates moved or left after having trouble following school rules. Pinto said attrition tends to be higher in a school’s first years, and that the high school lost just 2 percent of its students last year. (Charter school students aren’t bound by the city’s restrictive high school transfer policies.)

Of the 31 who graduated, all but one were accepted into a four-year college, according to state data. Eighteen months after graduation, two-thirds were on pace to graduate college within four years, Pinto said.

The network is experimenting with new approaches. Two Achievement First schools in New Haven, Connecticut are trying a model dubbed “Greenfield,” called that because the network’s CEOs said they “wanted everyone to imagine an open field with no structure built on it yet.”

Shanley, the board chair, said that the network’s Brooklyn contingent is interested in the model, which calls for students to spend up to 20 percent of the school year working on projects designed to expose them to real-world experiences. She said she’d also like to see Achievement First find ways to offer high school students college-level courses and internships through partnerships with colleges and companies.

For all of their criticism, the former Achievement First students spoke fondly of their high school experience. Wilson said if he falls short as an actor, he wants to return to the network’s schools to teach. Gordon attributed her interest in public health to a CPR training class she took at Yale University, which the high school sponsored.

And after bristling at the school’s rigid structures, Black said they helped her “get my life together” as a senior and graduate on time.

“That’s because I stopped trying to beat the system and started working with it,” Black recalled. “But I did that at the last hour.”

Correction: A previous version misstated the college status of Achievement First’s graduates.