Which list is most useful for assessing a student's understanding of closed-syllable words?

The correct choice for assessing a student's understanding of closed-syllable words is the list that includes "bat, cat, mat, sat."

Closed syllables are defined as those that end in a consonant and typically contain a short vowel sound. In this case, each word in the selected list consists of a consonant-vowel-consonant structure, which exemplifies closed syllable formation. Each of the words—bat, cat, mat, and sat—features a single short vowel sound followed by a consonant, making them ideal for assessing a student's proficiency in identifying and pronouncing closed syllable words.

Other lists do not serve this instructional purpose as effectively. The first list contains function words that do not focus on syllable structure and do not feature the closed syllable format. The second list includes words that generally contain long vowel sounds or vowel combinations, which do not illustrate closed syllables. The list with "bot, sud, dex, vill" consists of words that may not all conform to the closed syllable rule, as they may include variations in vowel sounds. Therefore, the chosen option clearly aligns with the goal of assessing proficiency in closed-syllable words through relevant examples.