What should Mr. Reed do after realizing most of his students do not understand three-digit subtraction?

Providing reteach lessons to the whole class is appropriate in this situation because it addresses the issue at a systemic level. When most students demonstrate a lack of understanding, it indicates that the concept may not have been fully grasped during initial instruction. By reteaching the lesson as a whole, Mr. Reed can clarify misconceptions, reinforce the material, and ensure all students receive the same foundational knowledge necessary for understanding three-digit subtraction.

Involving the entire class allows for interactive learning opportunities, where students can engage in discussions, ask questions, and work collaboratively. Additionally, it creates a space where peers can help each other, and Mr. Reed can assess understanding in real-time.

While small group lessons and one-on-one instruction can be effective for targeted support, they may not be the most efficient approach when the majority of the class is struggling with the same concept. Also, simply providing worksheets for homework may not effectively address the misunderstanding, as it could lead to frustration and lack of learning if students are still unsure about the foundational skills needed for the task.