Filmed gradually while its young stars (Mason: Ellar Coltrane, sister Samantha: Lorelei Linklater) grew up. That’s the hook, and it would make for a fascinating movie regardless, but Linklater has dug into his Before Trilogy bag of observational non-dramatic tricks and built something great. There are big plot points and dramatic moments, for instance when mom Patricia Arquette grabs the kids and flees her abusive, alcoholic husband, but it focuses just as much on smaller moments, and it’s true to its growing-up concept by not having every event have a consequence (e.g. Mason picks up a gun and nobody gets shot).
G. Klinger in Cinema Scope:
The film’s title is somewhat misleading: if Boyhood certainly chronicles Mason Jr.’s experience, it also allows us to see Mason Sr. and Olivia mature alongside their son. Olivia herself resides at the core of the film, heroic for her resilience and commitment to her kids, and tragic for her inability to make suitable decisions for her long-term happiness. Arquette is so sublimely perfect, so believable as a single mom struggling with poverty (even maintaining the same bad haircut for much of the film), that when her character finally breaks down toward the end, she achieves the kind of saintly purity that one associates with certain Bresson characters.