The last straw for Mitsuko Yamada apparently was the acceptance of 2-year-old Haruna Wakayama at a top kindergarten when her own daughter failed to make even the initial, random cut.

So the 35-year-old mother, a former nurse and the wife of a Buddhist priest, decided to kill Haruna.

On Monday, while Haruna's mother was chatting in the playground of the kindergarten attended by the sons of both families, Yamada led her to a public toilet next to the school and strangled her with her own muffler, police said. She then put the body in a black bag, dropped her own children off with their father, took the subway and the bullet train to her parents' home in the countryside and buried Haruna in their back garden.

"I was thinking of killing her for some time," she reportedly told police after turning herself in. "I had various interactions with Haruna's mother. It was not something superficial, and there were psychological clashes over a long period of time. I cannot express it in words."

Japan, a country where violent crime is rare, has reacted with horror to the all but inconceivable notion of the mother of one toddler killing another toddler. The story dominated national newscasts and headlines today as the government voiced concern about the level of competition at "infant ages" and promised changes, if necessary, in the controversial system of school entrance testing for young children. For their part, educational experts and parents focused on the pressures felt by parents, particularly mothers, for their children to succeed.

"Exam War, Hotbed for Tragedy" was the headline on a long editorial in Yomiuri Shimbun. "It is known that about 80 percent of the children in Haruna's neighborhood have taken entrance examinations by the time they reach the school age of six. . . . There is no wonder that this kind of competition could brew an emotional conflict among mothers who frantically want to see their offspring admitted to prestigious schools."

The Wakayamas and the Yamadas live in Tokyo's Bunkyo Ward, in a neighborhood famous for its schools. A park there is named Education Forest, and a promenade is called Path of History and Culture. A top public women's university in the neighborhood has a kindergarten and passes its students up through junior high and high school.

According to reports that police did not deny, Haruna had gotten into the kindergarten. These kinds of highly desirable public kindergartens require families to live within a reasonable commute. They make a first cut of applicants by lottery, in this case picking 70 names from among 550. Yamada's daughter was not among the lucky ones. Haruna was, and took the exam, which is an interview. On Nov. 19, her name was on the list of 20 who were admitted. On Monday, by pickup time at her brother's kindergarten, she was dead.

A search for Haruna was launched, and Yamada joined in. But on Wednesday she confessed to her husband. He asked her to turn herself in, which she did a day later. Police took her to her parents' home and dug up the body.

Many Japanese reacted by noting that mothers feel too invested in their children's successes or failures. "This entrance procedure was for 2-year-olds, but 2-year-olds can't compete. So what is being contested is the mothers," said education critic Naoki Ogi. "The pressure on the mother is heavier than if she herself was facing the exam. . . . But to go to the extent of killing a child implies that there is more involved here than the entrance exam conflict."

Mika Fukuda, a mother of girls aged 5 and 2, lives in the neighborhood and said her older daughter had lost out in the same lottery a couple years ago, but she didn't take it personally. "It's the same as any other lottery ticket."

She said that mothers' lives are linked too closely with their children's. "There is such a strong identification with the child's life that sometimes the value of the mother is determined by it."

Education Minister Hirofumi Nakasone told a news conference, "If exam-taking from infant ages is becoming overheated, we must consider ways to prevent such a situation."

Special correspondent Shigehiko Togo contributed to this report.