These 400 words are the first words that educators focus on when students are first learning their words. These are words that have silent letters, silent vowel sounds, and/or consonant sounds that are different from the letters.
These words are also the first words that ELL (English Language Learners) are introduced to.
I recommend having copies of the lists on pieces of paper; this is to be used as a repeat sheet, where students can just go down the list to check their speed and accuracy of the words. Also make larger laminated flashcards of each word, and build the list of words that the students know.