When the student has a rather high level of vocabulary in English, the target language, he can be reading a novel or a reader, and inferring the meaning of new words from the context, so he doesn’t need to turn to the dictionary too often, just a few times.
As well the student doesn’t interrupt his reading, because he doesn’t have the need to stop it.
I would advise anyway to look up some words, from time to time, so he can learn those new words, in order to expand his range of vocabulary.
The very fact of stopping to look up a word in the dictionary can help him to learn more words. In this latter case he does something physical, which is looking up the word, and in this way more likely he’ll be able to remember the word, because he’s aware he’s looking up a word, and besides he can make the effort to memorize that word.
Even some students make up a list of new vocabulary in a notebook.
This is also a physical exercise and helps to learn, and to revise sometimes. This is the model of autonomous reader. / Photo from: steam-locomotive-no-999-c-1893-daniel-hagerman fineartamerica com