Well, obviously. But my point is that holding everyone back a grade into next year just isn't going to happen and they're going to probably extend the next school year to help compensate, or extend school days by 30-45 minutes per day. You otherwise create a flow mess. Where do all the incoming K kids go in fall if all the existing K kids stay in K? Even if you let the HS seniors go, those teachers don't just reassign to K! (Such different skill sets.)
If infection rate continues to accelerate, maintaining a low rate depends on (a) expanding testing and (b) ensuring that care can be provided. The big issue with "opening for business!" is that when a business has 20% or more of their staff out due to illness, it will also wreck the economy, and likely lead to 2% or higher death rates.
The problem with percentages is that they're impersonal. "Only 2%!" But, think through 100 of your family and friends. Name them. That's the percent in action. 2 are highly likely to die.