Since the UN started large scale surveys of adult literacy in the developed world in the mid 90's, politicians in all those countries that have English as their mother tongue have been at a loss to explain their appalling results.
In English speaking countries around half of all adults are not sufficiently literate to cope with basic reading and writing tasks, yet data collected on pupils leaving schools gives much more optimistic information about their literacy standards than later proves to be the reality.
Why is this? The fundamental problem is an erroneous belief. The belief is that reading tests are a good measure of literacy – they are not! Why are they not? Reading tests do not generally distinguish between words that are read using knowledge of how they are phonetically represented by the letters used to spell them and simple sight-memorisation of the whole word (i.e. taking a visual snapshot of the whole word without understanding the relationship of the individual letters to the actual word as spoken.) If you test pupils on a word reading test and subsequently set all the words 'read' correctly as a spelling test you will discover that, for many pupils, between 15% and 65% of those words that were read correctly are subsequently spelled wrongly! Reading Ages are therefore not only a very poor guide to actual reading ability, but bear hardly any relationship to spelling ability and therefore to writing ability.
For most of the 50% of English speaking pupils who subsequently end up as illiterate adults, if they are tested at any age beyond Key Stage One (infants) we find that they usually understand single-letter phonic decoding of the initial alphabet sounds and also cope with the common consonant two-letter spellings (ch sh th ck ng bb dd ss, etc.). Sometimes they also know what the two-letter vowel spellings ee and oo represent. Beyond this, the complexity of the English sound-spelling system has defeated them and they tend to approach it (very often fearfully) using a variety of irrational and spontaneous behaviours, which are often underpinned by such anti-phonic notions as 'silent' letters, to take one example.
The UK National Curriculum is, in part, built around a core of key words. As pupils with serious phonic difficulties grow older, they naturally adopt a strategy of attempting to memorise visually as many of the core key words of the curriculum as they can to help them cope in the classroom. Ability to succeed with this sort of memorisation is very varied, but by the age of eight, two to three hundred words have been memorised by many of these pupils, increasing to perhaps four to six hundred words by age eleven and getting on for a thousand by the school leaving age of sixteen.
Not surprisingly, many of these key words also appear in standardised reading tests. So the reading ages of these pupils appear to improve slowly throughout primary education rising towards 8½ or 9½ by the time of secondary transfer. The test results on these pupils are completely misunderstood by many educators and administrators, who believe that they are achieving relatively poor, but nonetheless lifelong, basic literacy skills. However, having struggled throughout their schooling, once that schooling is over and they are no longer faced with practising the words they have sight-memorised on a daily basis, what happens? They rapidly forget many of them and, on testing later as adults, end up with more accurately representative reading ages in the range 6½ to 7½.
The published data tends to corroborate the above hypothesis: How many children fail to get a good GCSE in English? In the 1997 OECD study, how many adults in all English speaking countries were found to be poorly literate or illiterate? How many adults did the Moser Report as being poorly literate? Every time the figures converge towards between 40% and 50 %.
Q: How can this parlous state of affairs be changed? A: Only by: (a) adopting an effective teaching system and then; (b) giving all teachers high quality training in how to implement it in the classroom; and, (c) developing accurate ways of measuring the process to ensure that all pupils make steady progress towards life-long literacy skills throughout the whole of their primary education (All pupils may be an over optimistic goal, but at the very minimum at least 96% should achieve proper adult levels of literacy).