A principal walking into a noisy classroom has a choice to make. Is the noise evidence of students engaging with each other and learning social skills? Or is it the mark of an out-of-control class?

Most elementary-school principals are accustomed to making that call when observing teachers in older grades, as part of the typical coaching and evaluation process. But the markers of a successful pre-K classroom are different and not always intuitive, experts say, and an increasing number of principals will be tasked with identifying them as the city’spre-K expansion kicks into gear.

“How do you know if you have a good person? How do you help her get better? Is it OK that teachers are on the floor?” said Sherry Cleary, director of the NYC Early Childhood Professional Development Institute. “Some principals might see that as a problem, when we see that as perfect.”