 During the 2005–2006 cyclocross season, Boom who just turned 20 years of age, scored several wins including a win ahead of Sven Nys in the Grand Prix Sven Nys as well as the win in the Vlaamse Druivenveldrit Overijse after Bart Wellens was disqualified for having kicked a spectator.Boom was beaten by Zdeněk Štybar in a sprint for the Under 23 World Championships but returned a year later to dominate the race and to win the Under 23 World Champion jersey.For the 2006–2007 season, Boom asked and received special dispensation to ride the Dutch Elite Cyclo Cross championships and became Champion of the Netherlands.