CEDAR RAPIDS — After 35 years of leading Washington High School — and nearly a half year after his office initially let a substitute teacher remain working there amid rumors she had an inappropriate relationship with a student — Principal Ralph Plagman said Tuesday he was asked to resign.

Plagman, 72, announced his resignation and retirement in an email to parents.

“As much as I love my job, I cannot continue without the support of the district,” he wrote.

Within hours, some 40 students — who are still on summer break — converged on Washington High to chant and wave signs in support of the principal. Even more expressed disbelief on social media.

Many said they’ll miss hearing Plagman’s catchphrase — “It’s a great day to be a Warrior” — in the hallways.

“Everyday when he walks around the hall, he’s someone who knows every single kid’s name,” said Lucy Ernst, a 17-year-old rising senior. “Knowing that he’s not going to be there for my senior year is very heartbreaking and hard to hear for me.”

District officials’ decision to ask Plagman to leave, he wrote in his letter, was a result of a monthslong sexual relationship between a Washington High substitute teacher and a 17-year-old student.

The sub, Mary Beth Haglin, 24, was arrested last month on a charge of sexual exploitation.

District spokeswoman Marcia Hughes said in an email Tuesday afternoon the district had “just became aware” of Plagman’s letter to parents.

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“The statement represents Dr. Plagman’s perception of events and is not an official District statement,” Hughes wrote. “Since the District’s investigation into this matter has not concluded, the District will not substantively comment on Dr. Plagman’s statement.”

Though Plagman and other administrators investigated rumors of Haglin’s inappropriate relationship in February and again in May, no one in the district ever contacted police, district officials have said. The district also failed to keep Haglin from teaching in other schools after she was removed from Washington May 17.

In interviews with The Gazette after her arrest, Haglin admitted to having sex with the student and asserted the district wanted to keep her conduct “hush-hush.”

Superintendent Brad Buck, who could not be reached for comment Tuesday, told The Gazette last week that was so Haglin could leave the school with some dignity.

Plagman also could not be reached for further comment Tuesday.

“I have been advised by professionals with particular expertise in school law that I have done nothing unprofessional, unethical or illegal in the matter involving a substitute teacher’s inappropriate conduct with a student,” he wrote.

Plagman and at least one other administrator investigated Haglin’s conduct in February after hearing rumors of an inappropriate relationship between her and a student. The rumors were determined to be unfounded in an investigation that lasted a day, district officials said.

A second investigation was conducted after a video of Haglin and the student was posted online a few months later.

Plagman takes responsibility for those investigations in the letter.

“When I first learned about suspected inappropriate conduct in February, I did my best to perform a prompt and thorough investigation, and to make decisions based on the available information,” he wrote. “When additional information surfaced in May, I worked with school district administration to again take prudent action.”

District officials said no documentation for the February investigation exists and would not answer questions about documentation of the May probe.

Cedar Rapids police said they opened their own investigation of Haglin on May 30, and she was arrested July 22.

Plagman’s ties to Washington are strong after 35 years heading the school. He earned a $150,940 salary last fiscal year and has worked in the district for 49 years — the longest tenure in the district.

Many parents and some grandparents of current students remember Plagman as their own principal.

Tom Wilcox, a 42-year-old Washington High 1992 graduate, was outside the school Tuesday supporting his daughter and son as they rallied.

Wilcox said he was stunned to receive Plagman’s email and called his ouster an injustice.

“It’s the district saying, ‘How do we detract from the media attention and get someone to take the fall?’ ” he said.

Alumni and students plan to throw a bigger rally at the school at 4 p.m. Wednesday. An online petition urging Buck to rehire Plagman had more than 1,200 signatures late Tuesday.

“I pictured his last year as a series of applause and celebration,” Wilcox said. “A victory lap.”

In closing his letter to parents, Plagman wrote that the “safety and best interests of all students and staff members have always been my top priority.”

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“I love Washington High School, where I have been principal for 35 years and one month, and all of the thousands of students, staff members and parents whom I have been blessed to know and serve over all of those years,” he wrote. “It has been (a) tremendous honor and joy!”

Read Plagman’s full statement:

Dear Washington Community,

I wish to announce my retirement from my position as Principal at Washington High School effective August 3, 2016. Although I had intended to continue in this position for the 2016-2017 school year, the Cedar Rapids Community School District has asked me to step down from this position, and I have agreed to do so.

I have been advised by professionals with particular expertise in school law that I have done nothing unprofessional, unethical, or illegal in the matter involving a substitute teacher’s inappropriate conduct with a student. There has been significant media coverage regarding this matter, and I wish to comment briefly on it. When I first learned about suspected inappropriate conduct in February, I did my best to perform a prompt and thorough investigation, and to make decisions based on the available information. When additional information surfaced in May, I worked with school district administration to again take prudent action. Due to the ongoing nature of this matter it would be inappropriate to respond further.

The safety and best interests of all students and staff members have always been my top priority, and I have never, in my 49-year career with the District, done anything to jeopardize that. As much as I love my job, I cannot continue without the support of the district.

I love Washington High School, where I have been principal for 35 years and one month, and all of the thousands of students, staff members, and parents whom I have been blessed to know and serve over all of those years. It has been tremendous honor and joy! I also have wonderful memories of my earlier years at Kennedy High School and Metro High School. In my retirement I will continue to be the #1 fan of the Washington Warriors!

All the best to all of you!

DP