Dr. Freda Rebelsky, 78, activist and gifted teacher at BU

“The only thing I knew I didn’t want to be was a teacher,’’ she said in 1994 in a speech to the American Psychological Association. “I couldn’t see how anyone filled the time!’’

Then she took a summer course with the famous child psychologist Bruno Bettelheim and made a less than stellar first impression when he asked to borrow her course syllabus one day in class. “I was one of those kids who always sat in the front row,’’ she told the Globe in 1970.

Glancing at the syllabus, Bettelheim saw she had scribbled “Brutalheim’’ in the margins. Nevertheless, in conversations he soon saw her potential and offered her work as a counselor outside the classroom, defining a path that would lead her to become the first woman tenured in Boston University’s psychology department.

Dr. Rebelsky, who led the faculty union for a dozen of her more than 30 years as a BU professor and was an outspoken activist for progressive political causes, died of heart failure July 20 in Iowa Methodist Medical Center in Des Moines. She was 78 and had moved from Newton to Iowa last year to be near her son.

“She was a model of somebody who was an activist on campus and also an absolutely sterling teacher,’’ said Howard Zinn, the author and activist who was a colleague at BU. “Her students spoke of her with absolute awe. If you had to name the three or four best teachers at BU, she was always among them.’’

Seven years after she joined the faculty in 1962, 400 students signed up for an 8 a.m. class she taught in child psychology. For lack of space, another 100 were turned away. She served cookies to everyone at the first class and routinely invited scores of students to visit her Newton home on weekends.

“She felt it was important for her students to see she was a real person and to understand that faculty were more than just faculty,’’ said her son, Samuel of Grinnell, Iowa.

The students did, and so did her colleagues, who often honored her work. She received a Metcalf Award for Excellence in Teaching from BU, and the E. Harris Harbison Award for Gifted Teaching from the Danforth Foundation. In 1970, the American Psychological Association’s foundation recognized Dr. Rebelsky for her distinguished contributions to psychology education.

“Freda was the kind of person who couldn’t walk into a room without changing it,’’ said Gerald Koocher, a former student of Dr. Rebelsky’s who is dean of the School of Health Sciences at Simmons College and a former president of the American Psychological Association.

“She did some things that were certainly never done at BU before,’’ he said. “For example, she would hire a student who had gotten a good grade the previous semester to sit in the front of her class and take notes. Then she’d make copies and distribute them to her students so they could sit in the class and listen and participate in the discussion, instead of taking notes.’’

Freda Gould grew up in New York City, “in a left-wing family in a left-wing community,’’ she recalled in the 1994 speech. Her family lived in a union cooperative housing project in the Bronx, and she said she attended her first protests “in utero,’’ when her mother picketed for a neighborhood cause.

Among Dr. Rebelsky’s earliest memories was of sitting atop her father’s shoulders at an anti-Fascist rally in Manhattan.

Early experiences in activism with her family left an impression. “I have repeatedly seen that my voice is louder, clearer, more forceful when I join with others,’’ she said in the speech.

As recently as three years ago, when Dr. Rebelsky celebrated her 75th birthday, she was protesting the war in Iraq and participating in e-mail campaigns calling for the impeachment of President Bush.

“Activism is in my blood,’’ she told the Globe in March 2006.

“She was a very powerful and positive influence on so many people she encountered,’’ Zinn said, “a great model of somebody who will not remain silent in the face of authority or the presence of injustice.’’

During childhood in New York, she attended the Ethical Culture Fieldston School in New York City before heading to Chicago, where she worked with children with autism and mental illnesses after that first course with Bettelheim. While finishing a master’s degree in psychology at the University of Chicago, she met William Rebelsky.

They married on Jan. 1, 1956, and his work at Polaroid Corp. brought them to the Boston area, where Dr. Rebelsky received a doctorate from Harvard University in 1961. The following year, she began teaching at BU and “found my vocation,’’ she said in the speech.

“She would engage the class in rigorous discussion and wanted to hear everyone’s point of view,’’ said Koocher, a student of hers in the mid-1960s. “And she was constantly vigilant about what was happening in the class. If she saw someone dozing off, she’d say: ‘Everybody get up and stretch. Let’s open the windows.’ She was in the moment with the students; she wasn’t just someone lecturing at the blackboard.’’

Dr. Rebelsky played cello and painted, danced and wrote poetry, in addition to her academic books.

According to her speech, she would say to her students: “You have many multiple interests and abilities. Instead of worrying about them, realize that they are all you, they are all connected to a central core.’’

She began playing cello as her husband, who died in 1979, was being treated for cancer. Even in recent years, as her health declined, Dr. Rebelsky celebrated her own multiple interests with organizations and individuals she encountered, including at the Mayflower, a retirement community in Grinnell where she had lived since last year.

“I was talking with one of her friends here who said, ‘Freda seemed to learn a new thing every day and wanted to share everything she learned,’ ’’ her son said. “She always felt that people needed to remember to pay things back, that if someone does a favor for you, you should do a favor back, or do a favor for somebody else. Charity needs to keep giving.’’

In addition to her son, Dr. Rebelsky leaves three grandchildren.

A memorial service will be held at 2:30 p.m. Sunday in the Law Alumni Auditorium at Boston University.