In the weeks leading up to the new school year in Massachusetts, the head of one of the state’s largest school bus transportation providers warned he was down 10 percent of his workforce. The shortage, he said, probably would disrupt routes and cause students to be late to school.

“I’ve been doing this for 33 years, and I haven’t seen anything like this,” John McCarthy, the chief executive of NRT Bus, told WGBH late last month.

By the time school began earlier this month, McCarthy’s predictions proved true. When the first day arrived, students experienced extensive delays or missed pickups.

On Monday, Massachusetts Gov. Charlie Baker (R) announced a solution — he is making 250 National Guard personnel available to fill in on bus routes.

“The safe and reliable transportation to school each day is critical to our children’s safety and education,” Baker tweeted.

School districts nationwide are feeling the shortfalls of a dwindling bus driver workforce. Although districts often run into driver shortages, the coronavirus’s highly contagious delta variant has exacerbated the problem. While some drivers found other work when school shifted to remote learning last year, others may be wary of driving a bus filled with unvaccinated children. Many bus drivers are retirees, according to the children’s ride-hailing service HopSkipDrive, putting them in an age group that is more vulnerable to the coronavirus.

School districts have had to get creative with their recruitment of new employees — many launched social media campaigns that advertise a decent hourly wage and benefits.

Some are offering hefty bonuses to entice people to apply. A Montana school bus contractor is putting up a $4,000 bonus for first-time drivers, according to the Helena Independent Record. In West Michigan, one district is offering a $2,500 signing bonus and $500 to any employee who referred a new hire. A charter school in Wilmington, Del., is offering parents $700 for each of their children they can drive to school for the entire year.

Baker is the first governor to tap the National Guard to help alleviate the problem.

Beginning Tuesday, 90 Guard members will be dispatched to school districts in the cities of Chelsea, Lynn, Lawrence and Lowell, according to a statement from the governor’s office. They will receive training to drive passenger vans “to ensure the safety of children and families.”

Lowell Public Schools Superintendent Joel D. Boyd said in a statement that the district will be assigned 15 Guard members who he expects will be ready to get behind the wheel by the end of the week.

“This relationship will continue until we can fill all of our buses and vans with permanent school bus drivers,” Boyd said.

Chelsea Public Schools will also have the help of 15 Guard members, Superintendent Almi G. Abeyta said in a statement, noting that they will be unarmed and in uniform.

“This will ensure that students are picked up for school on time and returned home on time, so that they can have a productive day in school,” Abeyta said.

It is unclear how many members will aid Lawrence and Lynn public schools.

National Guard units saw more mobilizations in 2020 than any time since World War II, fueled by protests, wildfires and the pandemic. In many cases, Guard members were assisting overwhelmed health-care workers with coronavirus testing and vaccinations. They have again been called on in droves in recent months to relieve a dwindling hospital workforce dealing with a surge of critically ill covid patients.

A Washington Post-Kaiser Family Foundation poll found that roughly 3 in 10 health-care workers have considered leaving their jobs because of burnout, stress or mental health issues.

In August, Oregon Gov. Kate Brown (D) said she was mobilizing up to 1,500 Guard members to aid hospitals overrun with covid patients by handling logistics, coronavirus testing and operations. The governor sent in more service members earlier this month.

Two weeks ago, Idaho Gov. Brad Little (R) announced he was sending 150 additional National Guard members to aid hospitals, just two months after he announced a plan to withdraw the troops.

And on Monday, more than 300 Kentucky National Guard members joined 100 who were already activated.