Ten sentences with a blank in each, in a large rounded font with a reading girl in the bottom corner. She is a nurse, we are in the park, I am hungry, the cat is under the table, you are my best friend, Tom is eight years old, my socks are wet, it is windy, I am not tired, they are at school.
The ten split cleanly across all three forms, so no child can pattern-match their way through. Two subjects are plural nouns rather than pronouns, and “my socks are wet” is the one that catches children who have learned are goes with we and they but have not yet connected it to a plural thing.