The Phase I plan, authored primarily by Charles Glenn, called for busing students from Roxbury to South Boston. South Boston was a primarily white neighborhood regarded as "the stronghold of opposition to desegregation," while Roxbury was "the heart of Boston's black ghetto."  Not surprisingly, this arrangement worried many people around the city, including Judge W. Arthur Garrity, who did his best to distance himself from the plan, placing responsibility for any violence that came from it squarely on Glenn's shoulders.
The school board implemented the integration plan in September 1974. Most schools integrated quietly. In South Boston, however, protestors "stoned buses, shouted racial epithets, [and] hurled eggs and rotten tomatoes."  Nine black South Boston High School students were injured when angry whites shattered the windows on their buses.  Even elementary school students were not spared from the violence. Ellen Jackson, who ran a community center in Roxbury, described the scene as a bus of elementary school students returned home:
When the kids came, everybody just broke out in tears and started crying. The kids were crying. They had glass in their hair. They were scared. And they were shivering and crying. Talking about they wanted to go home. We tried to gently usher them into the auditorium. And wipe off the little bit of bruises that they had. Small bruises and the dirt. Picked the glass out of their hair. 
The next day, Roxbury families formed an escort to accompany the children, and they did not experience any additional violence. Racial tensions, however, were still prevalent. On October 7th, a black man named André Yvon Jean-Louis was severely beaten when he drove into South Boston to pick up his wife, who worked in the neighborhood. Roxbury students reacted with "a wild rampage during which they stoned cars and attacked passing whites," forcing Governor Frank Sargent to call out the National Guard. 
As the school year wore on, many white families planned a boycott of the public schools, sending their children to tutoring sessions at night, where public school teachers, college students, and prospective teachers volunteered to teach.  Violence against the black students had not entirely disappeared either. One night, a prominent black leader received an anonymous phone call telling him not to send the black students to school the next day. Community leaders managed to intercept the buses just before they left for school, and the black children spent the day at the University of Massachussetts. It turned out that somewhere between 1,500 and 2,000 people had been waiting for the buses in South Boston. Had the buses arrived, the protestors had planned to turn them over and burn them. Racial tensions continued to escalate, according to Phyllis Ellison, a black student at South Boston's high school:
On a normal day there would be anywhere between ten and fifteen fights. You could walk down the corridor and a black person would bump into a white person or vice versa. That would be one fight. And they'd try to separate us, because at that time there was so much tension in the school that one fight could just have the school dismissed for the entire day because it would just lead to another and another and another.
You can't imagine how tense it was in the classroom. A teacher was almost afraid to say the wrong thing, because they knew that would excite the whole class, a disturbance in the classroom. The black students sat on one side of the classes. The white students sat on the other side of the classes. 
Racial tensions erupted on December 11, when a black student at South Boston High School stabbed a white classmate. White students ran around screaming "He's dead, he's dead. That black nigger killed him. He's dead, he's dead . . . Get the niggers at Southie."  An angry mob quickly formed outside the high school, screaming "Niggers eat shit."  The principal ordered the black students to go into the office and stay there, because the situation was so volatile that any black student found in the halls would be attacked. It was up to the black parents of Roxbury to get their children out safely, which they managed to do by sending three decoy buses as well as the two that would actually carry the children.
Although the black students did manage to finish the school year, the temporary Phase I plan was clearly less than optimal. But a new solution was close at hand. Throughout the turbulent school year, Judge Garrity worked on a permanent successor, the Phase II plan.