Boston Mayor Marty Walsh acknowledged Wednesday a modest rise in the rate of positive tests for COVID-19 in Boston in recent weeks, mirroring a statewide trend, but he cautioned that the latest numbers suggest “an uptick, but not an established trend” so far.

Walsh also spoke at length about the city’s still-developing plans to reopen Boston schools this September, saying that no final decision has been made on whether to start the school year with all-remote learning or a hybrid model in which teachers and some students would return to classrooms on a part-time basis.

A draft plan released by the Boston Public Schools last week has ruled out the possibility of students returning to classrooms full-time in September. The path forward will depending largely on local COVID-19 case rates, as well as the preparedness of individual school facilities.

Walsh said the city and BPS are busy implementing various new health and safety measures in school buildings, including plexiglass and vinyl separators for classrooms, ensuring each classroom has at least one window that can open, equipping schools with disinfectant sprayers, replacing filters in school ventilation systems, and installing “sanitation stations” at school entrances.

“Whichever route we take in September, we’re doing the work now … to make sure that every school will be safe for a return back to school,” Walsh said.

Walsh and Boston Public Schools Superintendent Brenda Cassellius have faced backlash over the draft re-opening plan from various constituencies in recent weeks, especially from the Boston Teachers Union, which represents teachers, school nurses and other school professionals.

BTU members, including BTU President Jessica Tang, have called on the mayor and superintendent to take the hybrid model off the table for now, arguing that BPS is unprepared to reopen classrooms without endangering the safety of students and school staff.

Walsh has pushed back on those arguments, calling a recent protest by the BTU a “political” maneuver. But the mayor had a more conciliatory tone Wednesday.

“It is a very fragile time, and I think that if we’re going to open schools we have to sell and explain to people how we’re going to get schools open,” Walsh said.

Walsh said he is having productive conversations with the Boston Teachers Union.

“Myself and the head of the teachers union — she’s my friend — we’ve had ... great conversations and passionate conversations,” he said. “At the end of the day we’re on the same page. … It’s about keeping our kids and keeping our teachers, and keeping our grandparents, quite frankly, safe.”

Meanwhile, Walsh said that the recent uptick in positive COVID-19 tests in Boston is a cause for close scrutiny, but not yet alarm.

The city’s positive test rate rose from 2.1% to 2.8% in recent weeks, dipping to about 2.5% over the last seven days, Walsh said.

“It’s an uptick but it’s not an established trend,” Walsh said. “These numbers still remain far below levels we saw during the surge in April and May, and they would not cause us to look at rolling back any of the openings that we’ve already had here in the City of Boston.”

Walsh also repeated urges for Boston residents to fill out the 2020 U.S. Census forms, saying that Boston’s response rate has fallen from past censuses and that an undercount of Boston residents could result in “disastrous” consequences for the city.

Besides representation in Congress, the census helps determine various federal funding streams.

Residents can respond to the Census online, at