No idea what's going on, or what this is referencing.

Parody of the Miseinen no Shuchou (The Children’s Declarations) segment from Gakkou e Ikou!. In that segment, students would shout out the feelings hidden deep in their hearts from the school rooftop.

Here's some example of the segment.
https://www.youtube.com/watch?v=hAh7NAlryZY

pikuchan said:

Parody of the Miseinen no Shuchou (The Children’s Declarations) segment from Gakkou e Ikou!.

Here's some example of the segment.
https://www.youtube.com/watch?v=hAh7NAlryZY

Oh yeah! They did this in Kuroko no Basuke. Thanks.

And this is the actual scene from Gakkou e Ikou! 2015 3-hours SP here.