The Drew Elementary School teacher called her kindergarten pupils to the front of the room to write vacation words on a large sheet of paper. She led the 5- and 6-year-olds in a song-and-dance routine. She ushered them into small groups to work at learning stations around the colorful room decorated with their work.

One would hardly know that Nelson, a great-grandmother still sprightly at 78, had reached a milestone of milestones. When the day ended, she didn't just bid farewell to another class of soon-to-be first-graders - she brought down the curtain on a teaching career that had lasted longer than any other in the 25,000-employee School District of Philadelphia.

Fifty-one years.

"There's a lot of high-octane gasoline left in this tank, but I think approaching age 80 I should leave while my health is excellent, while my mind is lucid and while I can walk out of the classroom knowing that I have contributed a service to children and their families and the community - rather than being carried out on a stretcher," Nelson said, after parent volunteers had whisked her pupils to the library.

Her tenure would be noteworthy in any school district. But in Philadelphia - where tough schools and tight pay regularly conspire to chase teachers away - it's unheard of. No one in recent memory has taught for so long, and with such distinction.

"She's a very fine teacher, and the children are going to be left out in the cold, so to speak, without her," said teaching aide Vanessa Washington.

"When children have special needs, she tries to center right on them," Washington said. "And her caring and thoughtful ways and her sweet voice . . . ."

'She always continued to learn'

Drew Elementary's interim principal, Michelle Hayes-Flores, considers Nelson an inspiration.

"She seems happy every time she's with children," Hayes-Flores said, watching Nelson gather her pupils for a year-end class photo.

"Somebody who would give 50 years to a district to work with children, that's a wonderful dedication," she added. "I'm very proud, and I am very glad that I got the honor to meet Dr. Nelson."

"She always continued to learn," marveled Jerry Jordan, president of the Philadelphia Federation of Teachers, noting that even after earning a Doctor of Education degree, Nelson in 2002 became one of the city's few teachers to earn one of the highest teaching honors - National Board Certification.

"I think she's among a group of the last teachers who will put in a complete career with the school district," Jordan said.

"Younger teachers don't have the tenacity that Erlene has. They are not ready to put up with the disrespect, the large class sizes, the lack of support they get, and the salaries."

Nelson estimates that she has taught close to 3,000 Philadelphia children.

One of them, Monisha Das, a Bangladesh native, arrived during the 2002-03 school year speaking little English.

On Thursday, Monisha, who had completed fifth grade, stopped by Nelson's classroom to give her a gift of a large candle, and an even bigger hug.

Monisha, 11, recalled that her first-day kindergarten fears required her mother to sit in the back of the classroom - that is, until Nelson read her a story.

"As she was reading the story to me, I didn't notice that my mom went away because I was so attracted to the reading," said Monisha, in perfect English.

The changing child

Nelson began teaching in 1951 in Anniston, Ala., where her then-husband, a physician, was working. She taught third grade for a year before leaving the classroom to have two sons. In 1957 the family moved to Philadelphia.

In 1958 she became a kindergarten teacher at the old Gustavus Benson Elementary School, at 27th and Wharton streets. In 1968 she moved to Comegys Elementary, in West Philadelphia, where she stayed until 2002.

Benson served an all-black pupil population, most of which came from solid, two-parent households, she said.

"In the '50s, when I started, I had 30 children in the morning and 30 in the afternoon - and not one disciplinary problem," she said. "I could take 60 kids on a field trip without parents or any additional adults and not have one incident."

Of 24 pupils in her final class at Drew, in University City, she said, 10 live in homeless shelters.

Nelson said that she regrets the school district's shift from teaching kindergarten children primarily social skills to a "rigorous" math-and-literacy curriculum.

"Our students learn to be proficient academically, but deficient in social skills," she said. "So it's incumbent upon me to go beyond the core curriculum."

In retirement she hopes to write about parenting, and possibly consult on parenting issues for the school district and for other organizations.

"I see a need to nurture parents," said Nelson, whose two sons became physicians. Two of her grandchildren also become physicians; two others studied at M.I.T. and at Stanford University.

A life of achievement

Family is important to Nelson. Born in St. Louis, she was adopted as an infant by a Pullman railroad porter and his wife, who co-owned a hotel that served the city's black community.

Her father died when she was 4, and the financial strain caused her mother to lose the hotel and to seek work as a domestic.

In the segregated public schools of St. Louis, Nelson excelled - driven, she said, by a desire to honor her parents.

In 1951 she earned a teaching degree from the city's historically black Stowe Teachers College, where she was homecoming queen in 1947.

Over the years she earned an associate's degree from Philadelphia College of Art, a master's from Temple University, and a doctorate from Nova Southeastern University in Fort Lauderdale, Fla.

"My gift to my parents was to show gratitude," she said. "The way I could do that was to be the best person that I could be morally, academically and by keeping a kind spirit."