Rated PG-13. At suburban theaters

There’s no reason why Judy Blume’s game-changing 1970 Young Adult debut novel “Are You There God? It’s Me, Margaret” has taken this long to be adapted on the big screen.

But it’s finally here, and they did it right.

Faithfully adapted and directed by Kelly Fremon Craig, with Blume herself and James L. Brooks among the producers, “Margaret” continues to resonate because of its honestly realistic approach to its characters, both kids and adults, and its concerns which while set in the early 1970s remain timeless.

Margaret Simon (a winning Abby Ryder Fortson) is 11, a sixth grader suddenly transplanted from growing up in Queens, NY, to facing adolescence in the suburbs of New Jersey where she must make new friends, converse directly with God, get crushes and, most importantly, experience puberty.

Blume was a trailblazer in her realistic depiction of a middle school kid’s obsessions, whether it’s fitting in at school, worrying about breasts and menstruation or missing her beloved grandmother (a scene-stealing Kathy Bates).

Even before she starts school Margaret meets the bossy blonde queen bee Nancy (Elle Graham, very funny) who lives down the street and inducts Margaret into her “club.” Now with Janie (Amari Alexis Price) and Gretchen (Katherine Mallen Kupferer), Margaret makes its membership a quartet. Whenever Nancy breezily declares a mandate — that they all must wear bras for instance – all quickly agree.  But Margaret doesn’t need a bra yet – which leaves her seriously mortified. And leaves us laughing at her attempts to wear something she doesn’t need.

Margaret may have conversations with God but she’s been raised without a religion by her parents, due to their interfaith marriage.  Her mother Barbara (a vivacious Rachel McAdams) is a lapsed Christian with bigoted parents she hasn’t seen in years. Margaret’s dad Herbie (an engaging Benny Safdie) is Jewish. They decided that Margaret could choose her religion when she was old enough, so now Margaret is visiting synagogues and churches.

There’s a jab at gender expectations here as Barbara gamely tries to give up being an artist to become the best-ever suburban mom, signing up for every school committee she’s offered and gamely putting her paint brushes in the closet.

What works so well is the uniformly top-tier ensemble casting in even the tiniest parts like the many school classmates. And Fortson, a Marvel veteran, is nothing less than incandescent, giving Margaret a range of emotional textures while easily handling the physical comedy.

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