During the first week that her San Diego public school was shuttered to slow the spread of the coronavirus, not one of Elise Samaniego's students logged on to her virtual classroom.

Three weeks in, the teacher still had not connected online with roughly two-thirds of the students in her third- and fourth-grade combo class at Paradise Hills Elementary. She fears the pandemic will exact a devastating toll on education in the United States, especially at low-income schools like hers.

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"I do have several students below grade level, and this is just going to make it worse," said Samaniego, who has been emailing and calling families to get her 22 students to participate.

Teachers across the country report their attempts at distance learning are failing to reach large numbers of students. Hundreds of thousands of students are still without computers or internet access. Those who do log on have countless distractions: They are babysitting siblings, sharing laptops, lying in bed during lessons. Others log on only to walk away.

With schools closed for the rest of the year in at least 23 states, the uneven progress with remote learning is raising concerns that those who already were struggling will be left further behind.

"The pandemic is an educational equity crisis for vulnerable students who were too often underserved by our education system in 'normal' times," said Ian Rosenblum, executive director of The Education Trust-New York.

Not all schools are struggling. Those accustomed to technology transitioned smoothly. Derek Blunt, a math teacher at Making Community Connections Charter School in Keene, New Hampshire, said students are issued iPads in normal times and regularly use Google Classroom and other platforms. A week after the school closed, nearly all of his 65 students were doing their work.

In contrast, students at Samaniego's school faced several hurdles before learning could begin. Some only had internet access through their parents' phones.

"I can't tell them even where to start," she said. "Do you have a computer? That's step 1. Then you have to download Chrome. That's step 2."

Kelly Dighero, a 3rd-grade teacher at Phoebe Hearst Elementary School, holds up her laptop to block the sun during her first online meeting with students and parents on the front lawn of her home in Sacramento, California [Rich Pedroncelli/AP Photo]

In New York City, the nation's largest school district, tens of thousands of tablets and laptops have been lent to students, and the plan is for everyone to have a device by the end of April. Mayor Bill de Blasio said the district was still gathering data, but "there's clearly an issue with attendance".

That is true in many places.

In the Los Angeles Unified School District, the country's second-largest, as many as 40 percent of elementary school students had not logged on even once as of the first week of April - three weeks after the system closed.

As for those who have made an appearance, superintendent Austin Beutner, cautioned that "merely logging in does not tell us anything more than the student turned on their computer."

In ordinary times, some 16 percent of public school students nationally are chronically absent, with higher rates among high school, Black and Hispanic students, according to the US Education Department.

Many districts are now not tracking attendance because it tells them so little. But attendance is usually critical: Absenteeism is linked to a significant increase in the risk of dropping out of school.

And attendance is only one part of the puzzle.

Michelle Katz, a math teacher at the public Northridge Academy High School in the Los Angeles area, revamped lessons so they would work online. Most students in her Algebra II and pre-Calculus classes are doing their work. But only about half of her 10th-grade geometry students are logging on, and even some of them are not handing in assignments.

"When they were in class, you could get on their back and ask them about what was going on, where is the work?" Katz said. "It's hard from a distance."

Adding to her frustration was a student who interrupted a virtual class with yelling and profanity five times.

Schools are responding by making accommodations. San Diego Unified School District said this month is for working out the kinks, and instruction officially starts April 27. Some schools are adopting pass or fail systems or "no harm grading", in which grades will not be lowered during distance learning but can go up.

Given the difficulties of conceiving lessons and science labs that are effective virtually, some assignments feel like busywork to Emily Weinberg, a senior at Lexington High School, a public school in Massachusetts.

"I had to try to figure out what the kinetic energy of a dime was when I pushed it," she said. "I felt like this is wasting my time."

Even so, she is completing all her work.

Michelle Hansen, principal at Phoebe A. Hearst Elementary School, hands a laptop computer to the parent of a student that attends the school in Sacramento, California [Rich Pedroncelli/AP Photo]

But others are not and, in light of the challenges, some districts are ending the school year early, rather than leave many students behind. Many states are waiving the day requirements they set for this year.

Officials have not said what will happen in the fall, though there have been some calls to have certain kids who already were struggling repeat the year.

Dan Gannon, who teaches history at Bronx Leadership Academy, a public school in the nation's poorest congressional district, agrees lessons have suffered in shortened periods without teacher aides. Participation in his classes has vacillated between 50 percent and 80 percent.

Still, some learning is better than none, he said. Expectations need to be adjusted, but "that shouldn't stop us from trying to do some kind of teaching and some kind of learning."

This disruption is the second since 2018 for Achieve Charter School, which burned down in California's deadliest wildfire that devastated the town of Paradise.

Immediately after the fire, principal Steven Wright held morning assemblies via Facebook. He started them again after his school closed in March.

"What are we really hoping to teach kids?" Wright asked during one recent online assembly. "I don't think that those things that we talked about - in life, and entrepreneurship and how to be a better person and lead our world and be world changers - I don't think that teaching those things is limited at all by not gathering together for a while."