Monolingual or multilingual students with lowacademic language proficiency need to acquire conceptual understanding forpercentages and the language to communicate about them. The design researchstudy explores how these two learning goals can be fostered by amacro-scaffolding approach for seventh grade students. The dual hypotheticallearning trajectory starts from students’ prior experiences and guides them,via several levels, towards the mathematical models and meanings (conceptuallearning trajectory) as well as towards the necessary vocabulary for thinkingand communicating about them (lexical learning trajectory), linked by thepercent bar. For lexical scaffolding, the processes of offering, building andreflecting lexical means on different levels are focused. The qualitativeempirical investigations of the design experiments show in depth how students’conceptual understanding evolved together with the lexical means. For thispurpose, the interpretative reconstruction of semiotic chains is instrumental.