SAN JUAN, P.R. — Girls raced up the school steps in their plaid pinafores and backpacks on Tuesday, ponytails tied tight with colorful ribbons. They hugged and squealed and swapped dramatic hurricane stories, eager to catch up after more than a month away.

“We are ready,” Kenia Caraballo Rivera, the principal at the Dr. Francisco Hernández y Gaetan school in San Juan, said with a smile as students stopped to say hello or embrace her.

“And this,” she added, pointing to a beige folding table and chair in the main hallway near the entrance, “is my office.” With no electricity in the school and no windows in her office, Ms. Caraballo works in the hall, where daylight streams in through the front door.

The resumption of classes at the school on Tuesday was a joyous, achingly needed milestone on the plodding path back to normality in Puerto Rico’s newest era: After Maria. But the island’s education system is hardly picking up where it left off before the storm.

Only 98 of the island’s public schools reopened on Tuesday, 9 percent of the total, and the ones that did were in San Juan and Mayagüez, two major cities. Another 112 schools in those areas will open as soon as their final paperwork is turned in.

Few, if any of the reopened schools have generators, or internet access, or air-conditioning. School days have been slashed in half, at least for now. And the students — the ones who have not moved to the mainland — must bring their own water bottles and douse themselves in repellent to fend off the island’s mosquito invasion.