Students who earned straight A’s at Eastern Middle School in Silver Spring have been invited to a school dance Tuesday, a celebration that starts during the final period of the school day and includes a DJ, free pizza and a game room.

Students with B’s and C’s may join in later, when classes are over and pizza is no longer served. Students with lower grades are not invited at all.

Eastern’s “Academic Achieve­ment Celebration” is not an entirely new idea in education: Schools commonly reward student success. But the idea of a middle-school party that sets students apart by letter grades — leaving out 306 of the school’s 865 students, or 35 percent of the student body — has raised questions at Eastern and beyond.

Some parents say children should not be excluded from school activities, and others are wary of the straight-A emphasis. While parents say student achievement is important and worthy of recognition, the celebration has spotlighted the issue of how best to reward a school’s highest achievers.

“The students that don’t get to go end up feeling bad,” said parent Karen Hanlon, whose daughter has learning disabilities and was not invited to the party. Hanlon said the dance “separates the students into groups” in a school already divided between a highly competitive magnet program and the students who come from the immediate neighborhood.

Montgomery schools officials say principals have discretion about such events, and they point out that Eastern has other school dances and other ways to honor students. They did not say how common achievement dances are, though Eastern’s principal, Casey Crouse, said the celebration is not unlike others at Montgomery schools.

Chris Rutledge, the school’s PTSA president, said he views the event as one of many tools to encourage excellence. “I think it’s a twofold process: The school has to, and does, help all children to strive to excel,” he said. “And when they do, it’s important to recognize them.”

But Barbara Marinak, an associate professor of education at Mount St. Mary’s University in Emmitsburg, Md., who studies student motivation, questioned the celebration.

“You’re creating a caste system that could easily result in bullying and victimization, which is what we’re trying to prevent, especially in middle school,” Marinak said. She added, “We’ve got 30 years of research that says extrinsic rewards do little to nothing to nurture any kind of intrinsic motivation.”

The best motivators for students are relationships with teachers, leaders, peers and mentors, Marinak said. An event such as the Eastern dance is “a way to marginalize a ton of kids,” she said.

Crouse, the principal, said the intention is “a congratulations and an incentive.” She said reaction from teachers and students has been positive. Eastern had a similar dance when first-quarter grades came out in the fall, she said.

“The intention is not to make those who didn’t achieve feel badly,” she said. “This is to recognize those who did do well.”

Academically, middle school is important preparation for high school and college, Crouse said, and the dance is one way to show that hard work pays off. “You’re not going to get every job, you’re not going to win every race,” she said. “There’s something to be said for achieving something.”

She added that every student has an opportunity to earn an invitation to the party: “The hope is it’s an incentive to keep up the good work.”

Crouse also said the school has multiple ways of honoring students, including recognition based on qualities such as respect and responsibility. On Monday, students who reached certain levels of academic improvement were given a certificate and a snack.

“You don’t have to be an A-B-C student to get recognition,” Crouse said.

She said last week that she had not gotten objections from parents. One asked about a quiet place for a child who did not like dancing. Another parent asked about the school’s plan to issue wristbands showing which students met grade criteria.

That parent — Hanlon — raised concerns about students wearing such wristbands all day long.

“She brought a great point to our attention,” Crouse said, noting that the school was rethinking the timing of its wristband distribution.

Parent Lanita Whitehurst said she understands the principal’s hope to motivate students. But “if there is something about this that makes some kids feel excluded,” it might be time to reassess, Whitehurst said. “Certainly I would expect that kids who achieve well would be recognized, but the question is, is this the way to do it?”

Some parents worried that the dance could place unnecessary pressures on high-achieving students, who could fear exposure if they got a single B.

Parent Michelle Gluck said she appreciates the desire to celebrate academic accomplishment, much like athletic achievement. Still, she said, it might be better to include students with “big leaps in achievement even if it doesn’t result in straight A’s.”

Parent Caitlin James said she liked the idea of a school event as a way for students to celebrate and let off steam, but she said such an event should not be organized by letter grades. “It just feels inherently wrong to separate out the kids,” she said.

Mandi Mader, a parent in Garrett Park who treats adolescents as a therapist, said many schools post honor rolls in their hallways, but dances for achievers seem to go too far. “There’s already so much exclusion and grouping of kids,” Mader said. “Do we really need to make another one?”