I'm going to give the opposite to most responses
When little mine were told to keep quiet, head down and work.
It seemed okay through primary but when they got to secondary it was seen as not good.
There is a difference between a disruptive chatterbox and a confident child 'participating' in class dicussions unafraid to offer (confidently) viewpoints on complex, emotive and challenging topics.
It seems (now I'm out the other side) that this is a skill that needs to be learned and practiced and it aids our children to become confident speakers later in life.
Probably in the most part, they all come out of their shell eventually, but from experience, the encouragement and focus concerning this particular skill has served mine well.
It's not about being brash, too vocal, opinionated or inflexible in debate. It's about learning how to discuss topics maturely and appropriately - and confidently - and is expected of young adults wishing to enter universities and certain professions.
So, being the quiet mouse is okay to an extent, but watch out they don't end up fearful and nervous 18 year olds scared to open their mouths through 'lack of practice and encouragement' in their teen years.