Should we correct people's mistaken in grammar, pronunciation, spellings etc. as they speak or text?

From experience, the clear answer is - not at all. One should never try to correct people when they are in the process of talking.

It has the following effects -

• Makes the person feel inferior almost instantly
• Makes the person feel you're a complete idiot to not do it softly, indirectly, later
• Makes it a big ego issue and never achieves the desired result

Yes, even for a teacher, it is very tricky to do it in a class, as the student may be made fun of by others. This is a typical Indian habit, and an ugly one at that. The whole class may start giggling or smiling, and will make it miserable for the student concerned. So one has to then pull up everyone and teach them manners, not something to be done frequently.

So how should it be done?

1. Make a mental note of the mistake, when committed.
2. Indicate by your facial gesture (a minimal one) that you've identified something's wrong. (So other students who've realised it too, will know you're not ignorant of it)
3. Let some time pass.
4. Gently, softly, bring up that issue in a third-person tone ("Someone said a little while ago, and made this mistake while saying it, ... etc.)
5. It is important for the student concerned to know the mistake she/he made, and for others to know it too.

For standard errors, a teacher can address the class as a group, without anyone making a mistake. A classic case is of the word "definition". Most students spell it as "defination", which is clearly wrong. Another is millennium, that mostly is written "millenium" by people. One can go to the extent of explaining roots too - for example mill(a thousand) and enn (year) that would make it permanently fixed in their minds.