Why is the ninth month called September?
late 13c., "beginning," from Old French comencement "beginning, start" (Modern French commencement), from comencier (see commence). Meaning "school graduation ceremony" attested by 1850, American English. (Sense "entrance upon the privileges of a master or doctor in a university" is from late 14c.)
I know what you are thinking of -- the class members grouped in a semicircle on the stage, the three scared boys in new ready-made black suits, the seventeen pretty girls in fluffy white dresses (the gowns of the year), each senior holding a ribbon-tied manuscript bulging with thoughts on "Beyond the Alps Lies Italy," "Our Ship is Launched -- Whither Shall it Sail?" and similar topics. [Charles Moreau Harger, "The Real Commencement," "New Outlook," May 8, 1909]