**Figure 1** Screenshot of the Microsoft Office Excel spreadsheet used in the calculation of norms. Highlighted is the specific case mentioned in the description above.

For each grade (senior kindergarten to grade 3), the norms were calculated separately for both the symbolic and non-symbolic portions of the Numeracy Screener. In each case the number of possible raw scores were listed (1-56) in a column. In an adjacent column (refer to column D within Figure 1), the number of participants that achieved that raw score was recorded. In other words, the frequency with which this raw score occurred in the given sample was recorded. In the next column (refer to column E within Figure 1), the cumulative frequency was recorded. The final column (refer to column F within Figure 1) computes the percentile ranks using a formula that takes the cumulative frequency into account.

As an example, for the raw score of 32 (cell A33 in Figure 1) the following formula would be applicable: ((E32 (D33/2))/86)*100.

The frequency for the raw score being computed was divided by two and the product of this calculation was added to the cumulative frequency of the prior raw score. As we could see in our table D33 was divided by 2 then the product of this was added to value of E32. After this computation the product was divided by the total number of individuals in that particular grade (for our example 86 individuals) then the solution was multiplied by 100.