So there's a difference between teaching and motivating. A good teacher does both, of course, and not just with younger students. I think you're thinking about the motivational aspects of criticizing the kids?

There's a ton of research on how to motivate in the teaching environment. Some basics:

There's a big difference between extrinsic motivation and intrinsic motivation. Extrinsic means you are doing something because someone if rewarding you for doing it/punishing you for not doing it. Intrinsic means you are doing it because you, yourself, want to do it. In a classroom, grades are extrinsic motivation, interest in the subject is intrinsic. Both motivations work while they are present. But studies show that when extrinsic motivation stops, so does learning. That is, someone may do very well in a class to get good grades, but when they are done with the class they will stop learning the subject (if all they were in it for were the grades.) In the military, boot-camp motivation works while the soldier is being yelled at, but as soon as the sergeant goes away, so does discipline. (Deci, Edward L. and Richard M. Ryan, _Intrinsic Motivation and Self-Determination in Human Behavior_.) The key to getting motivation right is how the person being motivated views the reward or punishment. Or, in systems terms, you get what you measure.

This reflects on the method in the article. If the kids were learning chess to impress the teacher, they would lose motivation when they are criticised. But if the kids are learning chess because they want to win, they gain motivation when they learn ways to make that happen. Motivation is important.

Generally, it's better to be non-judgemental when offering a critique of students' work. I think she fails here a bit. But offering a critique is very important. If the critique is important, and the student wants to learn, then they focus on the content of the critique. The critique, also, has to be fair. If the critique is viewed as punishment, then the students might start attempting to please the teacher with theater. So if she called them lazy and they saw that as punishment for making moves too fast, they might engage in business-theater, making moves slower without thinking; this would allow them to avoid the punishment of being called lazy. But if she is correct in noting that they were, in fact, lazy, then they will recognize it as fair criticism and respond. (Kids are world-class judges of fairness, as all parents know.)

Also, students do much better (and are happier with) classes that demand high performance but allow them to work their way to success. (Clinchy, Blythe, "Issues of Gender in Teaching and Learning", Jrnl of Excellence in College Teaching 1 (1990):52-67.) The important thing is that the students feel some control over their ability to do better. (Also why you should never tell your kid "you are smart", this makes it sound like it's something they are, not something they do; i.e. something they have no control over.)

I think if you read any decent book on pedagogy (my favorite is "What the Best College Teachers Do", by Ken Bain) you'll see that there is a huge amount of research on how kids learn and how they are motivated to learn. That most of this research seems mainly ignored in the real world is unfortunate.