Elementary school students often misinterpret the equal sign (=) as an operational rather than a relational symbol. Such misunderstanding is problematic because solving equations with missing numbers may be important for the development of higher order mathematics skills, including solving word problems. Research indicates equal-sign instruction can alter how typically developing students use the equal sign, but no study has been conducted on the effects of such instruction for students with mathematics difficulty (MD) or how equal-sign instruction contributes to word-problem-solving skill for students with or without MD. In the present study, the authors assessed the efficacy of equal-sign instruction within word-problem tutoring. Third-grade students with MD (n = 80) were assigned to word-problem tutoring, word-problem tutoring plus equal-sign instruction (combined) tutoring, or no-tutoring control. Combined tutoring produced greater improvement on equal sign tasks and open equations than did the other 2 conditions. On certain forms of word problems, combined tutoring, but not word-problem tutoring alone, produced more improvement than did the control condition. When compared at posttest with 3rd-grade students without MD on equal-sign tasks and open equations, only combined tutoring students with MD performed comparably. (Contains 5 tables and 2 footnotes.)