George Grant, 14, added 41cm to his pole vault best with a 3.04m clearance in the Vault London event in Carshalton.
This performance lifts Shaftesbury Barnet Harrier Grant to ninth in the UK under-15 rankings.
His brother and team-mate, James Grant, 21, cleared 4.05m for his highest vault in five years at the London Games at Lee Valley.