"It's a skill that affects children's cognitive development. When they write, they build hand-eye coordination and practice fine motor skills," Zhang added.

Letter writing can be critically important for family relationships in helping to improve mutual understanding, especially between parents and children, according to Zhang.

His views were echoed by Cui Lijuan, a psychology professor at East China Normal University in Shanghai.

Cui said that in the past, most parental thoughts and views on a wide range of issues were "useful" and could be acted on repeatedly by children because society changed little from one year to the next.

But now, parents and children differ a lot, either in lifestyle or mindset, as many conventional parental views are challenged by children in an era of openness.

For teenagers broadening the number of people they meet, from just family members to friends, teachers and even strangers, parents are no longer their only sources of information, Cui said.

"Physiologically, the rapid development of the neural system in adolescence also results in emotional changes. Teenagers want both to rely on their parents and to break away from them, as they need more freedom."

As a result, Cui said writing a letter can help "everyone to calm down and think things over", as it is easy to voice negative views when feelings are running high.

But she said it is a process that involves pondering over every word that is used, and voicing heartfelt feelings to family members.