Year 4 students from a large metropolitan school in Melbourne were tested using the One Minute Tests of Basic Number Facts and a paper and pencil Number Screening Test developed by the author and colleagues. Observation of classes during the assessment procedures highlighted the vast difference in the students’ speed and accuracy when recalling basic facts and the types of strategies they used when solving whole number arithmetic tasks. When the results were analysed there were differences noted in the class results and when the results were presented to the teachers their reactions to these results varied considerably. This paper will focus on the comparison of the Year 4 class data.