MIAMI — A 15-year-old hatched a scheme with text messages to murder his mother with a 13-year-old pal, Miami Beach police said Saturday.

The hit, which detectives said was two weeks in the planning, failed when a steak knife the younger boy was using to stab the 51-year-old woman broke on her collar bone.

Police charged the son, a 15-year-old Columbus High student, with conspiracy, solicitation to commit murder and tampering with evidence. His friend, a 13-year-old Nautilus Middle School student, was charged with conspiracy, attempted first-degree murder and tampering with evidence.

The woman's son, police said, told the younger boy that cutting his mother's throat would serve as an initiation into his club, "Sons of Anarchy.'' The teenagers, police said, communicated by text to coordinate the ambush at Friday evening at a home in the 5700 block of Alton Road, where the son lives with the woman's ex-husband.

The younger boy tried to stab the woman eight to 10 times, police said, then fled after the knife broke and the other boy did not follow through on a pledge to join in with a box cutter.

Police said the boys confessed to the plot. The mother, who lives in Coral Gables, was treated at the scene for her injuries.