The "90210" star made one preschool teacher's life in Collingswood, NJ a helluva lot easier when he dug into his own pocket and paid off her Amazon Wish List of school supplies, and the awesome gesture couldn't come sooner with kids beginning classes next week.

The preschool teacher, Amy Hoffman, tells TMZ ... a few days ago she was watching Brian's first Instagram Live show that went on for almost 40 minutes. But, in the final 6 minutes or so, Brian talked about his kids and how they're handling virtual learning. He emphasized, now more than ever, the important role teachers play in our everyday lives.

And, with that in mind, Hoffman -- who normally has around 15 kids in her class -- says she decided to tag BAG on social media and direct him to her Wish List. And, get this ... Hoffman says that same day, Brian paid off her list, which came out to a little under $500.

Hoffman tells us with the COVID-19 pandemic, teachers are in desperate need of more school supplies because, unlike normal times, kids can't and shouldn't be sharing supplies.

Hoffman tells us she usually has a school supply budget of about $250 ... but teachers, on a good day, still have to pay out of pocket expenses to cover what they need. But, in the midst of the pandemic, teachers need individual tool kits more than ever -- crayons, markers, paper, etc. -- for every student to avoid potential spread of the virus.

We're told supplies started trickling in soon after BAG covered the expense.

There are TONS of teachers out there who need the exact same kind of help. And, just like Hoffman, one teacher in Illinois tried a similar approach ... but she hit up Amazon's head honcho, Jeff Bezos.