As students returned to classes Monday amid a continued surge in COVID-19 cases, Gov. Charlie Baker kicked off his week with an early morning press conference where he forecast "a challenging period of time" but called the reopening of schools a "terrifically positive sign about the hard work that so many people around the commonwealth are doing every single day to make sure kids get the education they're entitled to."

Baker visited Salem's Saltonstall School, where he said the "vast majority" of Massachusetts schools are open Monday. Some districts closed or opened late, including in cases where school officials said they wanted to use the time to test staff using state-secured kits that arrived later than anticipated or to assess staff availability levels.

"We fully anticipate that we're going to have staffing vacancies or shortages due to COVID," Salem Mayor Kim Driscoll said. "Frankly, that was the case before the holiday as well."

Brockton left its high school closed Monday, with other schools opening on a two-hour delay that district officials said would allow time to "assess staff absences that may be submitted in the morning." Woburn also delayed the start of its school day by two hours, a move intended to allow time for testing and ensure appropriate staffing.

The American Federation of Teachers Massachusetts had called for the new year to start with a period of remote learning "until the current wave of infections abates," and the Massachusetts Teachers Association had said that schools should stay closed Monday except for staff COVID testing.

Baker has stressed the importance of in-person instruction and said Monday that districts "do need to provide their kids with 180 days of in person education this year" and that districts can use snow days if they are not open at some point during the year.

"There was all kinds of talk last week about high school wouldn't open in Massachusetts today," he said. "School did, pretty much across the commonwealth. There are a very small number of districts that aren't in school. Some started late, but the vast majority of the school districts in Massachusetts — thanks to the hard work of so many people who were part of those school districts — are open today."