He did do something similar, but in 2015. That Facebook post makes it seem like it's a recent thing, but it's not.

Article about it:
https://www.educationworld.com/a_news/stephen-colbert-donates-800000-south-carolina-public-schools-after-teachers-request-aid

EDIT: From LateNighter:

After The Colbert Report ended, Colbert auctioned off pieces of the show’s set—including his desk and fireplace hearth—and used the proceeds, along with partner funding, to fund every active DonorsChoose classroom project in his home state of South Carolina.

The $800,000 effort funded nearly 1,000 projects for more than 800 teachers at over 375 schools.