Monolingual or multilingual students with low academic language proficiency need to acquire conceptual understanding for percentages and the language to communicate about them. The design research study explores how these two learning goals can be fostered by a macro-scaffolding approach for seventh grade students. The dual hypothetical learning trajectory starts from students' prior experiences and guides them, via several levels, towards the mathematical models and meanings (conceptual learning trajectory) as well as towards the necessary vocabulary for thinking and communicating about them (lexical learning trajectory), linked by the percent bar. For lexical scaffolding, the processes of offering, building and reflecting lexical means on different levels are focused. The qualitative empirical investigations of the design experiments show in depth how students' conceptual understanding evolved together with the lexical means. For this purpose, the interpretative reconstruction of semiotic chains is instrumental.