Darrell Desuze has been sentenced to eight years in prison for the manslaughter of pensioner Richard Mannington Bowes, at Inner London Crown Court.
Desuze's mother Lavinia, 31, was jailed for 18 months at the same court for perverting the course of justice.
Teenager Desuze, 17, punched the elderly man to the ground as disturbances swept the country on August 8 last year.
Mr Bowes, who had been trying to put out a fire in a dustbin near his home in Ealing, west London, suffered brain damage when his head hit the pavement. He died three days later in hospital.
Desuze, who can be named after an order banning his identification was lifted by a judge, admitted manslaughter last month.
His mother Lavinia, destroyed his clothing following the attack, and was sentenced during the same hearing for trying to cover his tracks.
Her son, who once enjoyed a school trip to the Metropolitan Police's riot training centre in Gravesend, Kent, where he watched a simulated riot with officers pelted with bricks, was caught on camera kicking in the glass doors of a shopping centre before joining a mob that attacked heavily outnumbered police with missiles around Spring Bridge Road.
Wearing sunglasses and a distinctive top saying "Robbers and Villains", he threw his full weight behind a punch to Mr Bowes's jaw, buckling his legs and knocking him unconscious.
The pensioner fell backwards onto the pavement and his head took the full force of impact on the road.
Prosecutors said police were "simply unable to reach Mr Bowes for some minutes because of the violence against them".
Mr Justice Saunders said the teenager committed the most serious crime in terms of its consequences during the summer's violence.
Alongside the manslaughter charge, Desuze has pleaded guilty to violent disorder and burglary at William Hill, Tesco Express, Blockbusters and Fatboys Thai restaurant on 8 August.