By ISMA’IL KUSHKUSH

MANDERA, Kenya — In a small classroom at Mandera Academy, a private school, posters with numbers, Swahili and English letters, and geometric shapes hung on the walls as dozens of students crammed together on small wooden desks.

Bilan Abdi, 9, stood up and spoke about her late teacher, Violet Muranga, who was shot last year as she was dragged out of a bus with other victims while traveling to visit her family.

“We learned a lot from her,” Bilan said softly. “Songs like ‘Twinkle, Twinkle, Little Star.’”

Kenya has suffered mightily at the hands of the Shabab, a Somali Islamist extremist group whose deadly attacks have left a painful void in this region’s schools.

Many of the 28 people killed on the bus, including Ms. Muranga, were teachers in the area heading home for Christmas break. Their deaths came around the same time as an attack at a mine in this northern corner of the country, where dozens of workers were separated by religion, forced to lie facedown and shot dead.

Farther south, nearly 150 people, most of them students, were killed this year in April when militants stormed a university in the town of Garissa. It was the nation’s worst terrorist attack since the 1998 bombing of the United States Embassy in Nairobi.

The shock, fear and continued sense of insecurity have caused dozens of schools to close. More than 1,000 teachers from other parts of Kenya have refused to return to teach in areas where they fear terrorist attacks, according to the Kenyan National Union of Teachers, igniting an education crisis in those regions.

“Yes, I am concerned,” the cabinet secretary for education, Jacob Kaimenyi, recently told reporters in Nairobi, the capital. “Why are the children in those areas not learning? It is because of conflict. It is because of insecurity.”

Many of the qualified teachers, especially for secondary schools, come from other parts of Kenya, or “down country” as it is known here. They teach math, Swahili, English and science.

“We have advised teachers not to go back,” said Wilson Sossion, secretary general of the Kenyan National Union of Teachers. “They are subject to attacks.”

At the Mandera Secondary School for Boys, almost half of the 32 nonlocal teachers refused to come back.

Ibrahim Hassan, the head teacher, explained that the school was able to fill the gap by bringing back “some of the bright boys from last year” to teach.

But he added, “We are worried.”

Keeping school doors open can be hard enough, but there is a bigger challenge as well: preparing students for the national exam that determines a student’s eligibility for a university education.

“I want the teachers to come back,” said Mohamed Kala, 20, a nervous, final-year student at the school.

Many worry that the number of teachers who refuse to return to Kenya’s northeastern region will only increase. Here in Mandera County alone, there is a shortage of 600 teachers, in a region that already historically suffered from neglect and poor educational facilities.

Only 10 percent to 15 percent of secondary students in this area score high enough on the national exam to qualify for a spot at a public university, according to local officials.

“You might not have a physics teacher in four years,” said Ismail Barrow, the Mandera County acting director of education, who has been in the temporary position for over a year.

Since 2012, more than 600 people have been killed in Kenya by the Shabab, an extremist group based in Somalia and affiliated with Al Qaeda. The group claimed responsibility for an April 2 attack on Garissa University College that killed 147 people.

“But the student has to sit for a physics K.C.S.E.,” he said, referring to the Kenya Certificate of Secondary Education examination. The exam is taken at the end of a student’s secondary education and determines access to a university.

Teachers say they are sensitive to the needs of their students, but many now fear for their lives.

“We choose life,” said Johnes Osoro of the North Eastern Down Kenya Teachers Association. “Many teachers are traumatized.”

Nyagaha Nicholas, 44, is the head teacher at Mandera Academy, which lost five teachers in the bus attack. He helped identify the bodies.

“I don’t want to remember,” he said. “The heads were shattered.”

“We are afraid, but we are supposed to be here,” he added. “The place is not secure at all.”

Public schools in Mandera have been hit the hardest. Schoolteachers are required to stay five years in a post before transferring, a prospect many now reject.

For private schools, it is a slightly different story. While security is a great concern, the lure of better pay is what brought some teachers to private schools here.

“Other teachers want to leave, but I am not likely to go,” Mr. Nicholas said, with a deep breath. “I’ve been here long. You can die anywhere.”

Outside the major towns in this region, a nomadic lifestyle dominates. Historically, nomads here have never been enthusiastic about sending their children to schools, as parents often require their children to help with raising animals.

That changed, local officials said, after recent severe droughts caused herds of livestock to perish, leaving families devastated. The country’s moves to decentralize the government and empower the regional authorities have also helped create a greater awareness of education, as local officials have emphasized the importance of going to school.

“Pastoralist parents started sending their children to mobile schools,” said Abdulatif Haro, head of Kotulo Ward, a subdistrict south of Mandera town.

Mobile schools move with nomads and provide basic education. Many of the teachers also came from down country, but now many have refused to come back to teach in them as well.

“Three mobile primary schools have closed,” Mr. Haro said. “And parents are taking their children out of some of the schools because there are no teachers.”

With the current challenges facing education in the county, some parents who can afford it are sending their children hundreds of miles away to the capital to continue their education.

Not everyone has that luxury.

“If I had the money, I would send Mohsin to Nairobi,” Abdirashid Ahmed, 47, a taxi driver, said of his 15-year-old son, who studies at a public school here.

The county government is trying to find solutions, though they are hardly ideal ones.

“We will use some untrained teachers until there is a solution from the central government,” said Mr. Barrow, the county’s acting education director.

Some of the teachers recognize the difficulties local communities now face in their absence.

“We are sorry for them,” Mr. Osoro said. “These are extreme circumstances that require extreme measures.”

The national government says it is looking for answers.

“What are we telling the people in those areas? Are we telling them that your children should not learn?” the education secretary, Mr. Kaimenyi, told reporters. “That is why it is important to work together to ensure that children in all parts of the country are able to learn.”

Suada Farhan, a 16-year-old student at Mandera Academy, was taught by three of the teachers who were killed in the bus attack.

“I cried,” she said.

Now, she said, the insecurity caused by Shabab attacks in the area is threatening something else as well.

“They are destroying our future,” she said.