Purpose: This study investigated understanding of mathematical equivalence in children with and without specific language impairment (SLI). Method: A total of 34 children (ages 8;1 [years;months] to 11;7), including 9 with expressive SLI (E-SLI), 8 with expressive and receptive SLI (ER-SLI), and 17 age-matched typically developing (TD) children completed addition and mathematical equivalence problems. The problem-solving strategies revealed in solutions and in gestural and verbal explanations were coded. Results: The children with SLI were less accurate than their TD peers in solving addition and equivalence problems. None of the children in the ER-SLI group solved the equivalence problems correctly; however, the number of children who solved any of the equivalence problems correctly did not differ in the E-SLI and CA groups. Children in the ER-SLI group tended to express incorrect strategies for solving the equivalence problems in both gesture and speech, whereas children in the E-SLI group often expressed "correct" strategies in gestures, but "incorrect" strategies in speech. Conclusion: Children with SLI showed delays in their knowledge of mathematical equivalence. Children with ER-SLI displayed greater delays than children with E-SLI. Children with E-SLI sometimes expressed more advanced knowledge in gestures, suggesting that their knowledge is represented in a nonverbal format.