Distribution of Reading Achievement
The PIRLS reading achievement scale was established in PIRLS 2001, based on the achievement across all participating countries, treating each country equally. The scale has a typical range of achievement between 300 and 700. A centerpoint of 500 was set to correspond to the mean of overall achievement in 2001, with 100 points set to correspond to the standard deviation. Achievement data from each subsequent PIRLS assessment have been reported on this scale, so that increases or decreases in achievement may be monitored across assessments. PIRLS uses the scale centerpoint as a point of reference that remains constant from assessment to assessment.
The results show that a number of countries performed quite well in PIRLS 2016, with 34 countries having higher achievement than the centerpoint of 500. The results also reveal that although the differences from country to country were small, there was a substantial range in performance from the top-performing to the lower-performing countries.