Unless the materials for this group of students are well-suited to their ability, regression will occur. The following anecdote illustrates this well.
A student who had been progressing well surprised me when she had two consecutive disappointing remedial reading sessions. When I discussed this matter with her parents, I learned that she wasn’t using the book I provided for home use but was using a library book that she had chosen. Unfortunately, as it was beyond her ability, it tore away at her confidence. This in turn led to a significant decline in her reading performance. However, once things were straightened out, she was quickly back on track.
Parents, should you need assistance finding suitable materials, seek advice from your child’s teacher.