The Japan UNESCO Association Federation launched the "UNESCO World Terakoya Movement: Write-and-Send Postcard Campaign 2018" in December. See the official website for entry details.
The Federation promotes the UNESCO World Terakoya Movement, which aims to expand learning spaces (terakoya) worldwide for children and adults deprived of educational opportunities due to war, poverty, and other reasons.
This campaign, part of the Terakoya Movement, transforms "treasure troves" lying unused at home—such as discarded postcards, unused stamps, and unused prepaid cards (QUO cards, telephone cards, bookstore gift cards, etc.)—into donations. It began in 1990 and marks its 27th year this year.
Eleven unused postcards can fund one month of education for one child in Cambodia. In 2017, approximately 1.08 million unused postcards (worth about 50.76 million yen) were collected from prefectures nationwide, enabling the completion of one terakoya each in Cambodia, Afghanistan, and Nepal. Over 4,000 children were able to receive an education.

Mirvachakot Temple School (Afghanistan), completed in December 2017

Literacy class for women (Nepal)

Terakoya graduates studying at middle school (Cambodia)

*As of June 1, 2017, the standard postcard rate has changed to 62 yen.
Postcards, stamps, and prepaid cards are accepted year-round, but collection efforts are intensified during the New Year's card season from December to May.
Recruitment Video (Click to play)
Unfinished Postcard Campaign 2018 Official Site: http://www.unesco.or.jp/terakoya/kakisonji2018
Related Series: UNESCO World Terakoya Movement Report
https://dentsu-ho.com/booklets/162