The teenage thug launched the attack on cabbie Harkawaljit Sarkaria in Denmore Gardens, Moseley, making off with his wallet with £250 in it, Wolverhampton Crown Court was told.
The attacker, who had marked his 14th birthday just weeks before, was also later found with a Taser disguised as a torch by police.
He was given an 18-month detention and training order – around half to be served behind bars.
Mr Howard Searle, prosecuting told the court how the teenager opened the front door and snatched Mr Sarkaria’s wallet after a row over the fare but was pursued by the victim.
The defendant then pulled out a knife and started stabbing Mr Sarkaria around the shoulder before another passenger joined in kicking the victim and jumping on his taxi.
Two passers-by rushed to help detaining the young suspect until police arrived at the scene.
Mr Sarkaria has made a recovery but remains fearful of strangers in his taxi after the August 22 attack, the court heard.
The other older youth was dealt with separately.
Judge Michael Challinor told the younger defendant, who admitted wounding with intent, possession of a disguised firearm, robbery and possession of a knife: “It is shocking that someone as young as you is facing such serious offences.”