One of the volleyball players who Kate joined for a quick game was particularly taken with the Duchess.
"She did really well and picked up the sport really quickly," said 16-year-old Grace Lazard. "I just feel really privileged and honoured to have played with her."
"She was playing in heels, whoever plays in heels is amazing," added the promising volleyball star who had played in an international tournament in Denmark earlier this week.
The new mum herself acknowledged that her footwear wasn't the most appropriate.
"I must remember to bring my trainers next time," Kate told SportAid's Chief Executive Tim Lawler, "This is great fun."
After her impromptu game of volleyball Prince William's wife then talked to teenagers taking part in the other sports before she was visiting various sessions where the promising athletes were given coaching in other aspects of their career.
Kate became patron of SportsAid this year.
The charity has provided invaluable help to some of the UK's top athletes Sir Bradley Wiggins, Sir Chris Hoy, Jessica Ennis-Hill, Tom Daley,David Weir and Paralympic swimmer Ellie Simmonds.