Updated at 4:10 p.m.

Gov. Charlie Baker issued new guidelines Thursday to help schools prepare for returning students classrooms in the fall, but the guidelines left broad questions unanswered about when and how a return will be possible.

Baker said the plan was designed to balance the risk of going into schools versus the risks of continued remote learning.

“Continued isolation poses very real risks” to the mental and physical health of children, Baker said.

The initial guidelines released by the state Department of Elementary and Secondary Education Thursday said the overall goal is “the safe return of as many students as possible to in-person school settings,” but the department acknowledged that there remains significant uncertainty about the trajectory of coronavirus infections in the commonwealth.

For now, school districts will be required to prepare reopening plans by August that address three possible scenarios: “in-person learning with new safety requirements, a hybrid of in-person and remote learning, and the continuation of remote learning.”

In-person learning remains the primary goal, the department said, because the quality of learning in-person is better than that of remote education and “In-person school plays an equally important role in our ability to support students’ social-emotional needs, including their mental and physical health, and in mitigating the impacts of trauma.”

And while schools do not appear to have been a significant pathway of infection so far, the guidelines require significant health and safety measures to protect students and teachers. Everybody in a school building above the second grade will be required to wear masks — though there will be exceptions for people with medical conditions, and “mask breaks” will be scheduled into the day.

Social distancing in schools will be less strict than in other public spaces, with minimum spacing of three feet between desks, rather than the six feet generally required in public, but schools are being urged to serve meals in classrooms rather than cafeterias when possible.

Schools will not be required to conduct temperature checks, but parents will be asked to screen children for COVID symptoms, and the state is working to ramp up flu vaccinations among students to mitigate the prospect of concurrent flu and COVID outbreaks.

The state effort makes clear that back-to-school planning will continue to evolve throughout the summer as public health conditions change.

“Districts and schools must be prepared to be flexible and ready to pivot if circumstances change significantly,” the guidance warns.

The "hybrid” approach that the guidance requires would have students taking turns in the school. Elementary and Secondary Education Commissioner Jeffrey Riley said one group of students would return to the building while others continue to learn from home, and then “they would switch — whether that is week on/week off or different days of the week is to be determined.”

The state is proving an additional $202 million in coronavirus relief funds to schools for COVID-related expenses — on top of hundreds of millions of dollars of COVID relief funds that have already been provided to cities and towns — and also providing $25 million in technology grants to bolster remote learning.

With that money and the new guidelines, Baker said, "school officials have the information and the resources they will need to implement the needed distance requirements, classroom configurations, mask and face covering requirements and symptom checks to make this all happen."

Riley said additional guidance for school districts will be coming in July, including instructions relating to school transportation and fall sports.

At the moment, there is broad skepticism about Massachusetts residents that in-person learning will be possible in the fall. In anew Suffolk University pollfor WGBH News, the Boston Globe, MassLive and State House News Service, less than half of respondents said they believe schools will be able to safely reopen.

Some teachers were critical of Baker's reopeing plan. The American Federation of Teachers - Massachusetts issued a statments saying "from expecting students to provide their own masks, to addressing how students will travel to school safely, to recommending only a 3-foot minimum physical distancing requirement, this guidance doesn’t adequately reckon with the realities, or the added costs, of reopening schools in the communities we represent."

The union suggested that the guidance would be more useful in weathy communites than poorer ones. "Opening schools without the proper safety measures, and the funding required to implement them, will only contribute to a resurgence of the virus in the same high-poverty communities that have already been affected the most," the group wrote.