One of the only experiments that has directly distinguished these two types of knowledge in a motor skill context was reported by McPherson and Thomas (1989). They classified nine- to twelve-year-old boys as "expert" or "novice" tennis players based on length of playing experience and tournament play. Novices had never played in tournaments and had only three to six months playing experience. The "experts," on the other hand, had at least two years of experience and had played in junior tournaments.