This story was corrected at 7:15 a.m. April 25. An explanation follows the story.

At Richard Montgomery High School, students in the Middle Years Programme are learning U.S. History in the same class as Advanced Placement students, and one teacher at the school thinks student learning is being sacrificed.

Brian Donlon, a social studies teacher at the Rockville school, issued a formal complaint to the school administration Thursday that accuses the school of labeling the class both AP and MYP to satisfy MYP requirements and offer AP courses. The number of AP students at a school boosts its placement on the Washington Post/Newsweek Challenge Index, which ranks performance of schools nationwide.

The advanced groups were combined because of an error in registration, according to Richard Montgomery Principal Nelson McLeod and Montgomery County Public Schools community superintendent Donna Hollingshead.

Hollingshead said the school system determined the best solution was to put students in one class, and inform students and parents of the class instruction.

“It is not an ideal situation, but [it] was the best solution for the kids,” she said, “ … There was no ill intent or cover up.”

Donlon said the students’ learning is being sacrificed because the curriculums are different. Advanced Placement U.S. History teaches the nation’s history from 1607 to present, while MYP U.S. History begins at the Civil War in the 1860s.

The Advanced Placement Program is run by the College Board, and includes an exam that allows students to obtain college credit, while the International Baccalaureate Middle Years Programme is an advanced program for students in sixth through 10th grades focused on real-world skills and critical thinking.

Students in MYP did not have the option on their registration cards of selecting MYP U.S. History, McLeod said. Only AP U.S. History, U.S. History, or U.S. History Honors were available. Some MYP students selected to take AP U.S. History, he said.

“When this error was discovered in late August, the schedules had already been made and staff had been assigned,” McLeod wrote in an email. “Since we did not have the staff available to create an additional class, students (and their parents) had the opportunity of taking the class as an AP class, or taking it as an MYP class that would prepare them for an AP US History Exam.”

Donlon said he does not think the school accurately taught the AP curriculum. Donlon, a teacher in the school system for 18 years, taught AP U.S. History for seven years, but does not teach the course this year.

“I believe the actions by the Richard Montgomery leadership are misleading to colleges and universities about the rigor of courses taken by students,” Donlon wrote in the complaint.

The school’s PTSA president Vince Mickens said none of the group’s officers knew about the mistake, and officers met with McLeod Monday regarding the issue, he said.

He said, based on information from McLeod and Donlon’s complaint, it appears the situation was approached appropriately.

“We feel very confident about the way the school is run and even more than that I have a great deal of confidence in the Montgomery County school system and I would like to think that if there were something truly afoul that we are in the kind of school system that would have been all over it,” Mickens said.

According to McLeod, the class syllabus was sent to the College Board, and students followed the MYP instructional framework and met AP class requirements.

After Donlon filed a complaint with the College Board, the company told him that although the College Board is not an enforcement agency, it takes the rigor of AP courses seriously.

The College Board addressed the complaint with the school and the school system, who assured the board that AP requirements are being met, according to Deborah Davis, the director of College Readiness Communications at The College Board.

Representatives from International Baccalaureate did not return calls for comment.

Correction: This article was updated to correct the spelling of Brian Donlon’s name.