Montgomery County returns to classic A, B, C grades in most of elementary school. Ps, for proficient, were purged for all but those in kindergarten and first grade. (Mike Blake/Reuters)

The report cards in Maryland’s biggest school system left parents puzzled. They showed a wide range of elementary school subjects, but the same grade popped up again and again: the perplexing letter “P,” for proficient.

It was too vague for many parents, almost inscrutable.

One mother in suburban Montgomery County counted 80 of them on a fourth-quarter report card with a total of 84 grades. A father said his children stopped paying attention to grading reports altogether, so unvaried were the marks that filled them.

“The all-inclusive P,” said Cynthia Simonson, a Derwood parent and longtime PTA leader who advocated for change.

As a new school year begins, the Ps of yore are largely gone. The Montgomery system, outside Washington, has reverted to familiar grades such as A, B and C for its second- to fifth-graders. Ps were purged for all but those in kindergarten and first grade.

“I’m glad that it went back,” said Jennifer Wood, PTA president at Twinbrook Elementary. “I grew up with an A, B, C, D system, and I think probably most of the teachers did. It makes it an easier process to communicate.”

School district officials say they decided on the change after a long tryout failed to resolve complaints and glitches with the grading system, which included four main marks: ES (exceptional), P (proficient), I (in progress) and N (not-yet-making progress).

The top grade of ES was not well understood or used consistently, and some schools did not use it at all, said Niki Hazel, director of elementary curriculum and districtwide programs in Montgomery County.

Some parents joked that grades of ES were like unicorns: You heard they existed, but you never saw one. Some said they only saw them in P.E., art or music classes.

“They were an elusive bird,” said Vincent Russo, a father of three in Rockville who said he wishes report cards included even brief teacher narratives about performance.

Some families said under the P system — rolled out in phases and first used districtwide through fifth grade in the 2013-2014 school year — they did not know until middle school, when traditional grades were used, that their children were straight-A achievers or had been lagging all along.

Many said Ps appeared to mean anything from a low C through an A, so it was hard to spot student strengths, weaknesses and progress — and some kids lost motivation.

“We felt like it was time to make a change,” said Hazel, noting the system could also be challenging for middle schools as they sought to place students in classes. “Our hope is that our parents will be better-informed about their children’s progress.”

The grading system that debuts this fall brings back most of the letter grades the district used before: A, B, C and D. This time, there is no failing grade of E. Hazel said as the issue was discussed, the E was viewed as “a little too harsh” for the young students. A grade of “M” indicates missing data.

The deliberations follow a move Montgomery made some years ago to a “standards-based” grading system. The idea was to better reflect what students were taught and how much they learned and were able to do.

Report cards now divide broad topics such as writing into subtopics — language use, narrative writing, opinion writing — with the goal of giving more detail across content areas and more consistency.

Nationally, an increasing number of school systems have embraced such standards-based grading and report cards in recent years, said Thomas Guskey, a University of Kentucky professor who studies grading.

The trend has been positive, Guskey said, leading to a stronger connection between grades and academic performance. But sometimes adjustments are needed, he said. Ps can be a broad category, he said.

“You don’t have to get rid of letter grades, but you need to make sure their meaning is clear,” Guskey said.

Rick Wormeli, another grading expert, also noted the importance of separating academic performance from issues such as work habits or other student behavior, which should be reported separately. “The goal is to inform parents with accurate, honest communication,” he said.

Valerie Coll, a third-grade teacher at Flora Singer Elementary in Silver Spring, said the new grading system gives parents a familiar vocabulary.

“It certainly puts grading in a format that looks like the report cards parents had when they grew up,” she said.

Kari Primozic, a mother of three in Gaithersburg who did not mind the P-dominated report cards, said she could see benefits to adopting the traditional set of grades, especially among older, elementary-age students.

“I don’t think anyone was harmed because they got a P instead of a B,” she said. But she said the A through D grading would help fifth-graders as they look to transition to similar grades in middle school.

But the change has sparked new concerns.

Colleen Reed, a Rockville parent, said a return to classic letter grades could increase performance pressure on young students, as parents react to grades with more anxiety.

“Sometimes, it’s pressure that’s not helpful for the kids,” she said.

Others question the new elementary report card’s grade definitions, which are different from what exists for middle and high school. They wonder if an A or a C, for example, will mean what parents think it does — or if there will be confusion anew.

The new report card for second- to fifth-graders describes an A as “consistently” mastering grade-level standards, while a B means “frequently” doing so and a C for “periodically” reaching that benchmark.

“They don’t match up with what parents understand,” said Michelle Gluck, a longtime PTA leader who has followed the issue closely. “It is misleading, because the grades describe standards that are different than what students will be expected to achieve in order to earn the same grades in middle or high school. An A has meant excellent for literally centuries.”

For older students, report-card definitions refer to levels of performance, with an A meaning an outstanding level, a B considered a high level, a C an acceptable level, a D a minimal level and an E an unacceptable level.

Montgomery officials said a committee of parents and educators will meet this year to discuss feedback, and definitions could be tweaked for next year.

Simonson, the Derwood mother and a vice president of the countywide council of PTAs, said she is glad for the change and will read her son’s fifth-grade report card with new interest this fall. She, too, is concerned about potential issues with grade definitions but said, “It’s a tremendous step in the right direction.”