It is an excellent strategy to group the students based on their level of understanding. You can then strategize on the best method to help students move forward in their groups. This is a great process because sometimes we feel that we fail as teachers. Analyzing misconceptions or mistakes in our teaching strengthens our skill and makes us better teachers. What was the lesson objective that your students struggled with and can you add more specifics to your lesson? I recently had students write a narrative story or what we call a brief moment story. The idea was that the story was to be a scene within a larger story. In essence, they were to write a description of something that happened in a fifteen minute window. Some students wrote a summary of something that happened over the course of a day. Having a summary group and providing a deeper explanation could be the difference between some students meeting and not meeting standards.