The current study investigated how prior knowledge moderated the effects of three educational technologies ("From Here to There," "DragonBox 12+," and problem sets in "ASSISTments") on seventh-grade students' later algebraic knowledge. Pretest scores only moderated effects of "From Here to There," with larger effects among students with higher pretest performance. Our findings have implications for understanding how prior knowledge interacts with design features within game-based applications to impact algebraic understanding. [This paper was published in: "ICLS2022 Proceedings," International Society of the Learning Sciences, 2022, pp. 2182-2183.]