Comparing only the first and last years in those patterns could lead to the conclusion that there has been no movement in the school's results. However, there was plenty of movement, either upward or downward, in the interim years. 1 Statistical significance testing is done to help determine whether group differences in average scores are very unlikely due to random fluctuation. If results are reported as significant, the probability of random differences is small. It should be noted that 'significant' does not always mean important.
Small differences can be statistically significant for large groups.
For example, for groups of 5,000, an 8-point difference in the SAT Total score is significant. It is debatable whether that is an important difference on a scale that ranges from 400 to 1600. Another advantage of analyzing multiple years instead of just two years is that the number of students in the analysis is larger. This is important because it reduces the chances that 'significance' was the result of a few extreme cases. Four of these schools showed upward trends, with two schools consistently upward and two schools significantly upward with some reversal during the interim years.