Miles Alura, 16, from Camden, north London, committed armed robberies in London and Kent while he was dressed in elaborate disguises. He was handed a five-year jail sentence yesterday.
The schoolboy, who left his history homework at one crime scene, adopted ambitious disguises for the robberies, dressing as an old man to steal £50,000 worth of stock from a jewellers in Longfield, Kent, on July 3, this year.
Alura, who wore facial prosthetics, make-up and grey hair pieces to disguise himself as an elderly man, produced two handguns and tied up terrified staff and a dog while he and a 15-year-old accomplice stole the goods.
A member of the public called the police and Alura was arrested in a nearby garden and the 15-year-old boy was arrested in a field three miles away.
The robbery led detectives from the Metropolitan Police's Flying Squad police to link Alura and a 16-year-old accomplice with a robbery committed at a jewellers in London, the previous month.
Alura wore false waist-length dreadlocks when the pair entered the Mayfair shop on June 7 and pretended they wanted to discuss custom jewellery.
Instead they jumped over the counter and threatened staff, pretending they had a gun, and tied the workers up before escaping with £100,000 of jewellery.
Police found fingerprints belonging to them both on paperwork - including school history homework and a drawing of the plan of the store - which was left at the scene.
Alura was jailed at Kingston Crown Court for five years after admitting conspiracy to rob, two-and-a-half for possession of an imitation firearm and five years for robbery, to run concurrently.
Neither of Alura's accomplices, who also admitted the charges, can be named for legal reasons. The 16-year-old, from Stoke Newington, London, was sentenced to three years in prison for robbery and conspiracy to rob, while the 15-year-old from Holloway, London, was given a 12-month detention and training order for conspiracy to rob and possession of an imitation firearm.