Systematic observation of how students approach a patterning task in class, as well as analysis of student work afterwards, may occasionally reveal that one or more students are lagging behind the rest of the class.
It may be helpful to interview these students individually to find out exactly what their difficulties are. Interviews can be given during a lesson while the rest of the class is working on other tasks.
Start with tasks similar to those done in class.
By occasionally asking a student "Why did you do that?" it is possible to tease out how they perceived the task and why they responded to it as they did. Some clarification can then be given before posing the student a similar task.
A year 3 student was slow at completing single-digit multiplication. By giving him two tasks in an individual interview, the teacher found out that he was still counting in ones.