What factor most likely disrupts a second-grade student's reading fluency?

When considering the impact of factors on a second-grade student's reading fluency, the lack of phonics knowledge is particularly significant. Phonics knowledge pertains to an understanding of the relationships between letters and sounds. It is foundational for decoding words effectively, which is essential for fluent reading.

Without a solid grasp of phonics, a student may struggle to sound out words, causing interruptions in their reading flow. This difficulty directly affects their ability to read smoothly and at an appropriate speed. As reading fluency is heavily tied to the ability to decode words quickly and accurately, a deficit in phonics can create significant barriers for the student, inhibiting their overall reading development.

In contrast, while vocabulary unfamiliarity, inability to understand language structures, and insufficient background knowledge can also impact a student's reading comprehension and engagement, they tend to have a less immediate effect on the mechanics of reading fluency itself. Phonics serves as the critical skill that, when lacking, most directly disrupts a student's ability to read fluently in the early stages of their education.