Mask requirements are returning in some school districts that had dropped them. Some are planning to vastly ramp up virus testing among students and staff. And a small number of school system are switching to remote learning. Educators hope that’s for just a short while, though. Soaring coronavirus infections mean the return from schools’ winter break will be different than planned for some as administrators again tweak protocols and make real-time adjustments in response to the shifting pandemic. Even those promising to bring students back as planned are signaling a need to stay flexible.