Sentence:  Madame could read with native grace and commendable fluency, making nimble <WSD>leapfrogs</WSD> over the heads of the exceptionally hard passages, but Leam had to spell every third word, and then she made a mess of it. 
Meaning of the word marked with <WSD> tags:  A game, often played by children, in which a player leaps like a frog over the back of another person who has stooped over. One variation of the game involves a number of people lining up in a row and bending over. The last person in the line then vaults forward over each of the others until he or she reaches the front of the line, whereupon he also bends over. The process is then repeated.