The younger of Hercules Wimbledon Athletic Club's Miller sprinting brothers, Chad, followed in his elder brother's footsteps when he smashed the club's boys U15 300m record in winning the event at the Merton Schools Championships at Wimbledon Park.
Chad, 14, was one of more than a dozen Hercules Wimbledon winners at the borough schools championships when he took the title in 40.1 seconds to eclipse the old mark of 48.19 set in the Surrey championships at Kingsmeadow in 2012 by Edward Grindrod.
It was the first time Miller, the South of England boys U15 indoor 60m silver medallist, had raced over the distance.
A few days earlier his brother Rechmial smashed the Hercules Wimbledon men's U17 200m record in clocking 22.04 seconds in an open meeting at Tooting Bec.
Miller junior collected a brace of titles at the Merton Schools Championships as he also took the U15 boys 100m title in a personal best of 11.93secs.
His Hercules Wimbledon clubmate Ralphael Buckle also clocked a personal best time in winning the boys U15 100m B race in 11.9secs.
It was an impressive improvement for 14-year-old Buckle who dipped under the 12-second barrier for the first time in improving on his previous best of 12.36secs set at the Hercules Wimbledon Young Athletes Open meeting at Wimbledon Park last month.
Buckle also took the 200m in 25.3 in his first race over the distance.
Both Miller and Buckle are competing in the 100m at the Surrey track & field championships at Kingsmeadow Stadium on May 24 and 25.
Molly McNamara-Langton gained a hat-trick of wins at the schools meeting.
The 15-year-old, who was competing in her first track meeting, won the girls U17 1,500m and 3,000m and the discus.
Fellow teenager Matthew Gibbons gained two titles taking the U17 boys 1,500m and 3,000m events.
He clocked a personal best of 9:56.97 in taking the 3,000m and was within a second of his lifetime best in taking the 1,500m in 4:40.3.
Two other Hercules Wimbledon athletes to gain wins were Chloe Lord who took the girls under 15 200m and 75m hurdles and Zara Hashmi who won the girls U17 100 and 300m titles.