For some Boston parents, the list of next school year’s "bell times" dropped like a bomb Thursday night.

This year, the opening bell at the Henderson School in Dorchester rings at 8:30 a.m. Next year, it will ring at 7:15. And that will make mornings tough on the family of 3-year-old Lucy Karp, who's enrolled in pre-kindergarten at the Henderson.

As they have redrawn bus routes and now school schedules, Boston Public Schools officials have called attention to the fact that every child’s trip to school involves a lot of variables. But Lucy’s case is even more complex than most.

“It takes us almost two hours to get out of the house,” says Lucy’s father, Roy. “We have all the typical things that a 3-year-old needs to get out the door in the morning: potty time, getting dressed, waking up, having breakfast -- all those things.”

Except that Lucy gets her breakfast through a feeding tube slowly overnight. She was born three months early, and has a history of chronic lung disease and acute respiratory distress. She travels to school with a walker and a pediatric nurse, the tube and other medical supplies in tow.

Lucy Karp, 3, during recess at the Henderson School. (Courtesy of Roy Karp)

The Henderson is Boston’s only K-through-12 “full-inclusion” school, meaning that students with special medical and behavioral needs are educated alongside "typical" students. Some parents choose it for that model, even those living miles away in West Roxbury, Roslindale -- where the Karps live -- and beyond.

As it moved quickly to reconfigure start times this fall, Boston Public Schools officials insisted they were forced to balance priorities. They wanted high schools to start later, so teenagers could get extra sleep, and for elementary schools to dismiss earlier, so young children could get home before sunset.

But the Henderson is a high school. And the district had also promised to make exceptions for schools like it — with “higher concentrations of medically fragile students or students with autism.”

So parents are asking: Why will it open so much earlier?

“I really don’t get the logic,” Roy Karp says. His family won’t feel it as much, he concedes, since he’s a stay-at-home dad. But the Karps still have to facilitate Lucy's afternoon feeding and to schedule Lucy's nurse.

"It's kind of unconscionable," says Leslie Candy, another Henderson parent, "given our delicate population. We're all confused as to why our times changed at all."

BPS Superintendent Tommy Chang said in a statement that the district changed start times "due to an abundance of research that shows student outcomes improve when secondary school students start later and elementary school students start earlier."

Before announcing the changes, district operations chief John Hanlon noted that they are dealing with a system of many moving parts and "1.8 octodecillion" different possible arrangements.

The district also pointed out outreach opportunities they have offered since last fall, including a survey that got more than 10,000 responses, community meetings and a website. (It's worth noting, though, that on the survey, members of the Henderson community, like the district at large, overwhelmingly preferred a start time between 8 and 8:30 a.m.)

In the background, the district is using an algorithm to trim its spending on transportation -- a persistent driver of its budget deficit. Finding those efficiencies, and staggering start times, may have led that algorithm to flip certain schools into a much earlier time bracket.

But to Candy, including Henderson makes this look like a decision made on autopilot. "I question the human aspect of the algorithm. Did anybody stop to think, 'Holy cow, this is a fully-inclusive school. Maybe we need to pull them out of the mix?' "

The Henderson community isn't the only one greeting a much earlier start with frustration. Under the new schedule, 17 schools — mostly elementary and K-8 — will experience an even bigger swing, opening earlier by two hours or more. (Five more will open at least two hours later.)

A petition protesting the changes was posted Thursday night, and had more than 4,500 signatures by Sunday morning. Many aggrieved parents say they support the changes made for high school students, but don't see why their own schools have to experience such a swing.

This year, the Mendell Elementary School in Roxbury dismisses its students at 4:10 p.m. Next year, that will move back 135 minutes, to 1:55 p.m.

That poses a problem for Mendell parent Patrick Banfield in picking up his son; both he and his wife work. Banfield says that given the long days he sometimes works as an attorney, "the thought of my 5-year-old son having to be at school for 11 hours [every day] is insanity."

Banfield says the new schedule may save the district money, but it could cost parents a lot: thousands of dollars more to cover all the additional after-school care. Those added costs, he says, could end up driving middle-class families like his out of the district.

Other parents worried about coaches and trainers for student-athletes. They won't be able to move practice earlier, since "they're working people, too," said Steve Sullivan, who has two kids at the Lyndon K-8 School.

Still others foresaw worsening changes in the rhythm of their children's days. Like Langdon White, another Henderson parent: "My kids already eat lunch — in heavy quotes — before 11 a.m. Does this mean they're going to be eating lunch by 10?"

The changes do have their defenders. Many high schoolers and their parents, in particular, celebrated online as their start times got later. (94 percent of the district's high schools will start after 8 a.m. next fall, as opposed to 27 percent this year.)

Even Henderson parents like Maggie Mancuso, who has three children there, said in an email she was "psyched they will be home earlier and I will have more time with them." Mancuso says she thinks parents are "freaking" out at the disruption but will find that things fall into place next year.

That's small solace to Roy Karp. His daughter is new to Boston Public Schools, but he already feels wary of the the district's "backwards" approach to thorny questions like this one.

"BPS does this a lot: announce major policy changes and then reacts" to family unhappiness, Karp said. "But it's a fait accompli! You've already announced the policy, and now you're just doing damage control!"

On its website, the district lists potential ways of coping with the new clock, including after-school programs, letters of explanation sent to employers and, finally, transfers to a new school.

But going back to the computer to readjust a single school's schedule isn't one of them.