In closing arguments at the trial against Jennifer Crumbley on Friday, lawyers for the prosecution and defense differed sharply over whether jurors should take the extraordinary step of holding a mother responsible for her child’s horrific crimes.

But both sides agreed on one point: This has been a singular trial.

Prosecutors are seeking to hold Ms. Crumbley partially responsible for the Nov. 30, 2021, shooting at Oxford High School in Michigan. Her son, Ethan Crumbley, who was 15 at the time, killed four classmates at the school and injured seven others, in the deadliest school shooting in the state.

“It’s a rare case,” said the Oakland County prosecutor, Karen D. McDonald, who accused Ms. Crumbley of negligence but acknowledged the high burden of proving beyond a reasonable doubt that she had committed a crime.

“It takes the unthinkable,” Ms. McDonald added. “And she has done the unthinkable, and because of that, four kids have died.”

Since last week, the jurors have heard wrenching statements from witnesses, combative debates between lawyers, and hours of testimony from Ms. Crumbley, 45. The charges against her and her husband, who each face four counts of involuntary manslaughter, are at the leading edge of a push by some prosecutors to hold parents accountable when they are suspected of enabling deadly violence by their children.

The husband, James Crumbley, 47, will be tried separately in March.

Ms. Crumbley’s lawyer, Shannon Smith, said that her client should not be punished for the bloodshed that her son set in motion, in part because Ms. Crumbley could not have foreseen what would happen. Ms. Smith also argued, using examples from her own life, that parenting could be a messy and unpredictable job.