Second language acquisition (SLA) researchers have long searched for patterning in the development of linguistic elements (e.g., grammar and morphology). However, little attention has been given to the examination of systematicity in vocabulary acquisition, limiting our understanding about how overall vocabulary is learnt. The current study investigates L2 learners' lexical knowledge to explore whether there exists a consistent sequence in the acquisition of vocabulary components in second languages. Written form/meaning-recall and written form/meaning-recognition knowledge of four word-knowledge components (form--meaning, collocations, multiple-meanings, and derivatives) was assessed on 314 EFL learners from two distinct L1 backgrounds (Chinese and Spanish). Implicational and Mokken scaling analyses revealed a reliable hierarchy of knowledge of vocabulary aspects where recognition knowledge preceded recall knowledge across all components. The scale remained constant across the learner groups when explored independently (using an 80% accuracy threshold) and collectively (under both 75% and 80% accuracy thresholds). This finding indicates that the various aspects of word knowledge seem to be learnt incrementally in a consistent order by EFL learners, regardless of their L1. The study offers an empirically supported framework of word-knowledge acquisition that improves our current understanding of L2 lexical development and can serve as guidance to further systematize vocabulary instruction in the EFL classroom.