This activity comes from Good Habits Great Readers. I found it an excellent way to elevate readers of all levels in first and second grade. Ignoring the ending on a "big" word and reading the "little" word really transformed a lot of readers. They first figure out the base word then add the ending.
The student cover "ing" with their finger, after figuring out "play" then tack on the ending and are now able to read a lengthy word. A great technique!