Research into vocabulary knowledge often differentiates between breadth (how many words a person knows) and depth (how well the words are known). Both theoretical categories are essential for understanding language learners’ lexical development, but how the different aspects of vocabulary knowledge interconnect has not received the same attention as each individual dimension, especially in terms of productive knowledge. This study analyses lexis from mid-frequency lemmas in the K3–K9 frequency bands from the learner corpus PELIC (The University of Pittsburgh English Language Corpus). Critically for learners, mastery of lexis in this frequency range is essential for achieving the English proficiency required for university study. From these mid-frequency items, a dataset of 7,554 tokens were collected from word families with multiple derivations and manually annotated. The findings showed high rates of collocational and derivational accuracy for the forms learners opted to use. However, compared to expert speaker texts in the Corpus of Contemporary American English (COCA), learners overused the verb forms and underused the noun forms of these lexical items. These patterns provide evidence of the interplay between breadth and depth in learners’ productive vocabulary usage, suggesting that increased lexical depth will naturally lead to greater lexical breadth and vice versa. Pedagogical implications reaffirm the importance of developing learners’ explicit morphological awareness and collocational accuracy. Suggestions for mid-frequency lexical items to prioritize in language learning are also provided, with a view to helping learners achieve academic readiness.

对词汇知识的研究通常区分广度（一个人知道多少单词）和深度（单词的了解程度）。这两个理论范畴对于理解语言学习者的词汇发展都是必不可少的，但是词汇知识的不同方面如何相互联系并没有像每个维度一样受到同样的关注，尤其是在生产性知识方面。本研究分析了来自学习者语料库 PELIC（匹兹堡大学英语语料库）的 K3-K9 频带中的中频引理的词汇。对学习者至关重要的是，掌握这个频率范围内的词汇对于达到大学学习所需的英语水平至关重要。从这些中频项中，一个 7 的数据集，从具有多个派生的词族中收集了 554 个标记并进行了手动注释。研究结果表明，学习者选择使用的形式的搭配和派生准确率很高。然而，与当代美国英语语料库 (COCA) 中的专家演讲者文本相比，学习者过度使用了这些词项的动词形式而未充分使用名词形式。这些模式提供了学习者生产性词汇使用的广度和深度之间相互作用的证据，表明增加的词汇深度自然会导致更大的词汇广度，反之亦然。教学意义重申了培养学习者明确的形态意识和搭配准确性的重要性。还提供了在语言学习中优先考虑的中频词汇项目的建议，