Is it right for principal to scold tracher on this?

I'm a teacher and in my school it is forbidden for a teacher to study while taking classes. However teachers has atleast 7 period in a day without any break and sometime it becomes impossible to stand for that long sometime we really even struggle to walk after standing for so long. One of the teacher in our school has knee problem still she is not allowed to sit. One time when she sat for a period due to severe pain the principal scolded her in front of the kids saying that she disappointed her. Even in the meeting today the senior teacher and principal targeted her by insuinating the fact that no one is allowed to sit and if further anyone sits they will remove all the teacher's chair from all the classes. I do understand why they are emphasizing this fact since they want teacher to be alert about what children are doing, however is it a right thing to do on their part?

I'm going to guess you meant to type "forbidden for a teacher to SIT while TEACHING." I've never heard of such a rule. Furthermore, the "senior teacher" (no idea what THAT is) and principal are woefully, terribly inept and unprofessional in chastising an employee in front of students. That would be true if the employee was the custodian or the janitor. "Praise in public, correct in private" is a useful concept, even in education. When I was in school, most teachers taught six classes in a seven period day. Most of them DID stand, most of the time, but sat if we were completing a worksheet, taking a test, or monitoring a study hall. Of course they sat during their own lunch breaks. I'm going to guess that a 'principal' who acts so unprofessionally is employed in a private or chartered school. He or she may have a lot of power, and as employees who aren't unionized, the teachers have little or none. In small, private schools, often teachers work "at the pleasure of the headmaster." Your choices are to acquiesce or move on, I guess. In an employment situation like you describe, right or wrong isn't relevant. The obvious compromise (a 30" high stool to sit on) won't work in an atmosphere like this.

I'm not sure what country you are in. But in the USA there is ADA (Americans with Disabilities Act). Businesses/bosses are required to provide reasonable accommodations to employees with temporary/permanent disabilities. And simply needing to sit occasionally due to a knee injury, would certainly qualify as a reasonable accomodation. Maybe your country has something similar?

Yes actually it is a private school and generally the principal and senior teacher who are there for more than 7 years or so have power but ultimately it's the chairman who has ultimate power over anyone and I must say he is most unreasonable person I have ever seen. And I reside in India, the govt. School doesn't has such restriction but private organizations functions According to the wishes of chairman and the next authority. There is law but the media doesn't always portrays the teacher in best of light we are always in the negative light. That's the reason we don't have any choice and we also don't have any way to speak up about our issues to the management because we know that they won't listen to us at all.