"It's a lie that mistakes are wrong!"

One thirds of students in a Grade5/6 split class were asked to stay classroom after school to take an additional math class. 
The teacher taught me that they have failed a test and need to understnad the basic part of multiplication. 

I found an interesting moment before starting the additional class. 
T (Teacher): "Do you know why you are here today? Because you made mistakes, right?"

S (Student): "Yeah..."
T: "In our culture, mistakes are often seemed to be bad. However, it is wrong! So, let's celebrate this opportunity to develop our brains!!! Hooooo!!!" (And crapped hands👏👏)
S: (seemed to a bit confused, but crapped their hands)

Although it should be borning, and students are easily reluctant to attend these supplemental classes, by doing so, students have less sense of failure and more positive attitude to keep challenging. 
I've never seen literally celebrating mistakes before. 

In the class, while the teacher asked questions to students and found a student is trying to answer the question, she said "See!! (student name)'s brain is developping right now! Go for it!" to everyone. 

I am not sure if I should tell it to my students  all the time, on the other hand, I believe it  helps students to capture mistakes in a different way. (Some nuroscientific studies also support this stetament according to another student teachers.)
That was really positive moments in the school! :)