Greta Gerwig's High School has 'Lady Bird' Fever

Greta Gerwig's critically-acclaimed "Lady Bird" -- which she wrote and directed -- figures to be an Oscar darling, but it's already a huge winner at her alma mater.

Greta's former high school, St. Francis Catholic High School in Sacramento, CA -- where the movie is based -- is totally stoked about Gerwig's success and not afraid to show it.

Sources close to the situation tell us Greta's parents heard the school was buzzing about "Lady Bird," so they delivered movie posters to the school and pins for the students to wear.

We're told if Greta or her movie get nominated for the Academy Awards -- which is more than likely -- the school plans to have an Oscars watch party for the big night and cheer her on.