Current research addresses students’ arithmetic and algebraic knowledge, focusing on conceptual connections, and relationships between two aspects of knowledge. The contents in question are rational numbers and rational equations in grades 7, 8 and 9. The tools for analysis comprised an algebraic concept of rational numbers, Kieran’s theory of generalizing arithmetic into algebra, and Kaput’s  theory about the relationship between arithmetic and algebra in a conceptual context. 

 Current research shows that students’ knowledge of algebra and arithmetic has a limited conceptual connection and a weak relationship with each other. Their knowledge of arithmetic operations and solving rational equations used to be solely procedural and relied on formulas learnt in a procedural – and often mixed – manner. This caused conceptual consequences for students’ knowledge of rational numbers and their essential properties, as well as shortcomings in students’ ability to operate with rational numbers. This study highlights that conceptual transitions from rational numbers to rational equations play a crucial role in students’ learning, focusing on the conceptualization of arithmetic concepts and their ability to operate in an algebraic context.