From the Boston Globe opinion piece (to be fair these authors are professors at the Harvard school of public health and, though obvious credible, view the issue though a particular lens):
"We are not advocating a return to schools as usual. Schools must aggressively implement proven risk reduction strategies. A layered approach should include rapid testing and contact tracing, physical distancing when possible, mask-wearing with breaks built into the day, frequent hand hygiene, and well-ventilated spaces. Districts should consider adding tents and trailers and converting gyms, cafeteria, and libraries to expand learning spaces. Staggering arrival and dismissal times and prohibiting parents from entering schools will limit one of the highest risks — having large numbers of adults in indoor spaces."
Additionally, if you link to the risk reduction strategies you will see a document suggesting exactly what I've been talking about - multiple ideas that are cost or structurally prohibitive that won't receive the necessary funding, community support or professional/political leadership required to implement successfully (please check pg 31 for an example).