These researchers say preschoolers do better at language if their teachers are confident in their own abilities, and it helps if the classroom emphasizes emotional support for the kids.
I suspect the principle in the first part is true of every human occupation. On average, people who think they can do something well are likely to do that thing better than people who do not think they can do it well. What I'm not so sure about is the extent to which the confidence causes the difference. It could be that they are confident because they are better. The only problem with this is the research showing that people who are not good at their jobs think they are.
But it does point out again that the single biggest school-related factor in a kid's development is the quality of the teacher. Parents, peers, and genes are important, too, but of those things that take place at preschool, the quality of the teacher-child interaction is the most important. ECERS, teacher education, staffing levels, and all those other easily measured things clutter up the view of that fact. What matters most is what happens between the teacher and the kid.
And I sometimes think this is one of those things you either get or you don't, that after two weeks on-the-job training in a high-quality center, you could separate the keepers from those whose gift is not early childhood education by watching them with the kids. But I also think an AA in ECE is enough to teach 4-year-olds, so what do I know?