Questions / instructions:

1. 17 - 9 =

2. 74 - 21 =

3. 52 - 37 =

Commentary:
On the questions which did not involve re-naming (carrying), about 70 percent of year 4 students and 90 percent of year 8 students were successful. Where re-naming was required, success rates dropped substantially for year 8 students and dramatically for year 4 students (whose incorrect answers are revealing). It is noteworthy that the 447 year 8 students produced 60 different answers to question 7.