And once more with feeling...

 Graduation from ??

No caption on this one,

but Sondheim attended the George School,

a private Quaker prep in Bucks County,

so shall we assume?

If so...1946.

 Coveting Bernstein's shiny suit, probably.

They worked together on West Side in 1956-57,

tho as the story goes, mentor Oscar Hammerstein had to talk

SS into doing just the lyrics.

 Huge fan (and collector) of games and puzzles...

"putting it together"!

 Sondheim contemplated a career in math at one point,

and mystery novel writing at another.

 With mentor and good friend,

Oscar Hammerstein.

At Oscar's urgings, Sondheim showed him an

early musical he wrote, which Oscar deemed lousy.

"Now, do you want to know why it's lousy?"

And thus began an education.

SS also worked with Milton Babbitt,

noted for his serial and electronic music

("a frustrated musical theatre composer").

 Collaborating with Richard Rodgers

on Do I Hear A Waltz?

 Congratulations

after success with Sunday in the Park with George.

Sondheim with Bernadette Peters and James Lapine,

who wrote the books for several Sondheim musicals:
Sunday, Into the Woods, Merrily, and Passion.

John Weidman (librettist for Pacific Overtures,

Assasins and Bounce)

 Sondheim, and Frank Rich.