Associated movements can be a variety of body movements that indicated that a child is trying to elicit more muscles to help with a task. Here are some examples:
Opposite hand that is doing the task trying to do the same thing
Posturing Core into flexion or extension
Here is an example, your child has just learned how to write their name. When they practice you notice they stick out their tongue or move their lips as if trying to form a letter with their mouth. It is common when adding a cognitive load; for example, copying letters that are written vs. writing dictated letters.
It is important to look at the cognitive load when you see associated movements. It can be a helpful indicator that child does not have a skill automatized and needs more practice.
Many times, we ask can a child write their name, color, make their shapes, and/or draw a person. It is important to look more than just a simple yes or no. If a child can write their name but you notice a lot of associated movements, it will likely be more difficult in a group setting. We usually “test” skills in a one on one setting although, kids rarely complete academic tasks in a one on one setting. For example, when a child is at school they are not just focused on writing their name; they are thinking about the directions the teacher just said, other sensory information in their environment (noise, body awareness, visual input), writing it on a variety of types of papers and where to place their name on the paper and attention to task. Therefore, if a child is demonstrating associated movements in a one on one setting they need more practice to be independent with skill in a school setting. It is a helpful indicator for quality and control of a task not just ability to do task.