Science of Vocabulary Scaffolding

In order to fully comprehend a text, students need to understand the majority of words in the text. Students learn most vocabulary through daily practice with language in writing, reading and speaking. For some vocabulary, there needs to be explicit and scaffolded instruction as to the definition and context of the word. 

A key way to ensure this, especially with domain specific vocabulary, or higher tier words, is through previewing key vocabulary. Studies show that when students are explicitly taught the definition, pronunciation and context of a word, they are more likely to remember that word and comprehend a text using that word., This positive effect on comprehension becomes heightened when words that are unfamiliar or difficult to define are previewed before diving into the reading. 

References: 
https://www.readingrockets.org/helping/target/vocabulary#:~:text=Vocabulary%20plays%20a%20fundamental%20role,with%20oral%20and%20written%20language.

https://www2.ed.gov/programs/readingfirst/support/rmcfinal1.pdf 

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/136457/rrq163_am.pdf?sequence=1