Six-year-old Samuel’s disruptive, dangerous behavior convinces his school that he’s a child out of control. The school’s administration wants to separate the boy from the other children.

His single-parent mother, Amelia, will have none of it. She pulls her child out of school instead. Increasingly, though, in Amelia’s own interactions with Samuel, he’s becoming a problem child for her, too.

Is Samuel a little demon? Or is there really a monster under his bed and in his closet, as the anxious, insistent child tells his sleep-deprived mother every night.

Samuel calls the monster the Babadook. “Mom! Mom! I’m gonna smash its head!” he screams.

“The Babadook,” the brilliantly creepy feature film debut from Australian writer-director Jennifer Kent, is among the most chilling, disturbing horror films of the past few decades.

Kent draws inspiration from silent horror films of the 1920s. She effectively revives the high-contrast photography and mood of dread that haunts classic German horror films “The Cabinet of Dr. Caligari” and “Nosferatu: A Symphony of Horror.” In “The Babadook,” the results are sleek, modern and edge-of-your-seat frightening.

Essie Davis plays Amelia, a woman whose classical musician husband, Oskar (Ben Winspear), died in a car accident nearly seven years ago. Oskar was driving the about-to-give-birth Amelia to the hospital.

Amelia and the child she named Samuel survived the crash. Afterward, the widowed young Amelia never celebrated Samuel’s birthday — it falls on the exact date of his father’s death. “My dad’s in the cemetery,” Samuel tells people.

In the days that follow Samuel leaving school, the mother’s and child’s lives fall step by descending step into nightmare. Davis’ Amelia experiences an alarming on-screen transformation. She goes from a normal young woman and loving mom to a frazzled wreak who looks older than her years.

The many trials little Samuel puts Amelia through would push even the most patient parents to distraction. Davis expresses the mind trip Amelia takes in awful yet strangely beautiful strokes.

Noah Wiseman co-stars as Samuel, a small boy with a big knack for disrupting the lives everyone around him. Wiseman, in his professional film debut, jumps instantly from sweet child to little devil. “The Babadook,” Samuel tells a little girl, “would eat your mum for breakfast!”

“The Babadook,” a small but hugely inventive horror story, is a monsterpiece. Some of the movie’s choices are inexplicable, but those minor, mood-enhancing tangents don’t stop the film from establishing Kent, an actress-turned-director, as a major new talent in the horror genre.