Answer: Using random assignment
Step-by-step explanation:
Random assignment is the mechanisms in which chance procedure is used while experimenting so that assurance about every participant regarding getting assigned certain group is same.In this research , participants are randomly assigned to the group so that each group has similar or equivalent characteristics.
According to the question,Professor Montgomery should use random assignment for her concern .She can randomly assign children to the new teaching method so that level of comprehension can be similar to receive equivalent result.