What does it take to become a star? In the fall of 1948, Marilyn Monroe had just a few roles in box office flops on her resume -- but LIFE photographer J. R. Eyerman apparently saw enough of a glimmer in the 22-year-old starlet to follow her through the showbiz training that promised to make her big.

The incredible -- and seldom seen -- images in this gallery are the first a LIFE photographer ever took of Monroe, though the magazine did not publish them at the time. (In fact, she wouldn't show up in LIFE's pages until October 1949, along with seven other then-unfamiliar Hollywood "girls"). But now, in celebration of what would have been Monroe's 85th birthday (June 1, 2011), LIFE.com presents these rare gems, restored to their original glory and showing early-career Monroe in the dance, acting, and voice classes that helped make her an icon for the ages. Here: Marilyn runs a hand through her long curls -- dyed but not yet that famous platinum hue -- in one of Eyerman's portraits.

Here are more photos of Marilyn Monroe: