Historically there has long been an interest in establishing whether children's reading levels have declined or improved in comparison with previous years. This would seem to be a valid research question and a potentially useful area of investigation. However, in reality it is a minefield. There are several reasons for the explosive nature of this topic.

First, reading holds a central position in children's education. Producing young people who are literate is the sine qua non of an adequate education system—the necessary if not sufficient demonstration that schools are doing their job. Thus, the measure of reading standards is seen as a proxy measure for educational standards more generally.

Second, the rise and fall of reading standards provides a focus for fierce debates about teaching methods, which typically crystallise around traditional versus progressive methods. Currently, the traditionalists champion methods of teaching reading that involve explicit phonics tuition. The progressive movement, sometimes referred to as “the real books approach”, emphasises the importance of purposeful reading for meaning and enjoyment. In practice it is established that eclecticism rules.

Third, there are differences of opinion concerning the most appropriate ways to assess reading levels. In order to plot reading standards over time, both valid and reliable methods of assessment are required. Preferably, too, the same test should be repeated, although parallel versions of valid tests can also be used. In practice this has frequently meant that tests involve either decontextualised word reading or sentence completion. There is agreement that such forms of assessment do not measure all the aspects of reading or literacy. There are those who argue that assessment that fails to take into account a wider range of higher-order skills, such as skimming, scanning, interpretation, and comprehension monitoring, and that uses only a narrow range of decontextualised text, will tell us little that is valuable about the level of children's reading. From this position it is difficult to measure reading standards validly over time. It is also argued that assessment should measure the areas of literacy covered by the curriculum and that as this changes, tests must also change, making comparability over time problematic.

Despite these debates, children's reading levels have been measured over time and even across countries. The question is how valid such exercises are and what conclusions we can draw from the results.