For the follow-up to their masterful 2011 drama “The Descendants,” Oscar-winning co-writers Nat Faxon and Jim Rash also assume the roles of co-directors in this beach and vacation coming-of-age comedy that rivals “American Graffiti” in scope, intelligence, knowing humor and emotional depth. Teetering between Disney channel hokum and precious art-house twee during its opening scenes, “The Way, Way Back” quickly regains its footing and strides confidently towards a riveting and richly-rewarding conclusion. Surrounded by a truly dream supporting cast, relative unknown Liam James stars as Duncan, a 14-year-old boy we meet at the peak of his awkward puberty phase. Pale, withdrawn, borderline anti-social with a major case of fumble mouth, Duncan is still reeling from his parent’s divorce and is none too happy with his passive-aggressive mother Pam’s (Toni Collette) lout of a boyfriend Trent (Steve Carell). It also doesn’t help that Duncan is forced to spend time with Trent’s …