In "My Fair Opponent" it appears that close-ups for the outdoor scenes at Fillmore Junior High, were done later on the Bradys backyard set. Here you see a two-shot with the Brady girls:
and then close-ups with Maureen McCormick were done inside on the Brady set with the backyard wall behind her.
In the following scene, the girls are still outside, and the close-up of Debi Storm was done inside in the same spot. (Even adding a water fountain and student extras walking by in the background).
(As reference, photos of The Brady yard below:)
Debi Storm, Eric Shea