Gavin joins the Great School Run
More than a million kids all over the UK are taking part in a massive race called the Great School Run.
Kids at 4,331 schools are running a 2km race this week, to encourage children to do some exercise every day.
Some of the races will have a special visitor, as ex-Olympian Colin Jackson is being flown around the country by helicopter to start them off.
This is the first time ever that the race has had more than one million kids taking part.
Hurdler Colin Jackson said: "This is the culmination of all the children's and their schools' hard work in training and preparing for the big finale event. I think a lot of children have proved to themselves that they can do anything if they put their mind to it."
Come back later to see Newsround's report from a couple of the races.