Schools in the Argentine capital began reopening Tuesday as part of a gradual return to in-person classes amid the pandemic.
Final-year pupils at around a dozen public schools in Buenos Aires returned to classes, the mayor's office reported.
"This is a very important step, reincorporating school to close a key stage in their educational life," said deputy mayor Diego Santilli.
Some primary school students are due to resume classes next week.
"Between state and private school management, 70,000 boys and girls are going to be able to attend face-to-face classes that will complement the virtual spaces," said Soledad Acuna, the top education official in Buenos Aires.
The classes will be held in open courtyards and in a "bubble" of 10 pupils per group, to prevent any outbreak from spreading beyond the circle, school authorities said.
The main teachers union has rejected the move to reopen schools, even partially.
The ADEMYS union demanded city authorities instead provide computers and internet connectivity to economically vulnerable students who have been unable to maintain links with their schools.
"As long as the pandemic continues, as long as the virus is circulating in the community, we are not going back to in-person school or any kind of in-person activity," the union said in a statement that called for a strike on Tuesday and Wednesday.
In-person classes were suspended in Argentina on March 15, just after the beginning of the southern hemisphere school year.
Since then, classes have continued virtually by Zoom and other internet platforms.
The return to classes announced last Friday is part of a move to relax confinement measures in Buenos Aires and the surrounding region, where nearly a third of Argentina's 44 million population live.
"It was quite nice. To see a blackboard, the see a teacher and not a screen, to have things explained to you, to write things down. It's weird but it's like coming back to real life," high-school student Lola Perez Costa, 18, told AFP.
Oscar Lazbal, principal of the Hipolito Yrigoyen National School of Technical Education, where Pope Francis went to school, said he was "very happy" to have students back.
"Not only in pedagogical terms but also emotional aspects. We are all happy to have them back here," Lazbal said.
The number of new infections has declined in the capital, though it still averages around 900 a day.
Infections are on the rise in some areas of the country, however, forcing authorities to reverse plans to reopen schools.
To date, Argentina has reported more than 903,000 coronavirus cases, with a total of 24,186 deaths.