The Los Angeles Galaxy player is in his native U.K. to visit family and he took time out to perform his duties as an ambassador for supermarket giant Sainsbury's 1 Million Kids Challenge.
The project aims to encourage a million children from across Britain to try a paralympic sport ahead of the 2012 Olympics in London in July (12).
And Beckham shocked youngsters at Vaughan Primary School in Harrow, north London by joining them as they tried their hand at various sporting disciplines.
He was greeted by an enormous cheer from the excited pupils as he walked into the school's assembly hall unannounced on Friday morning before joining them in the playround.
Beckham told TV show This Morning, ""It's been a while (since I've been to school). I've been in my kids' playgrounds a few times but it's been a while since I've been in one in London.
""I'm here as part of (my role as) ambassador for Sainsbury's, and we have got, like, a Sainsbury's Million Kids Challenge that has been going on. It's something that I'm very proud of. What's amazing is it's a Million Kids Challenge but there are two million kids around the country that have (joined in and) tried paralympic sports.
""That's inspiring for many people. It's great for kids to try different things that are going to be in the paralympics. It's a great thing.""