This notion of a vocabulary explosion may suggest that the optimal time for oral vocabulary development is in these toddler years. (aft.org)
Children with reading difficulties may show slower growth in oral vocabulary knowledge, as well as slower progress in reading and might need additional help when they encounter unknown words in texts. (tdtrust.org)
This can be thought of as a late effect of oral vocabulary — first you need to identify the words, then you need to understand their meanings. (teachermagazine.com.au)