If you need to use a word that may be unfamiliar, fluent readers may appreciate a glossary at the end of the document. For readers with greater difficulties, keep an explanation of the word close to where the word is used, either in brackets or in a new sentence. For instance, if you use counsellor in a low-literacy document, you may want to add that this is someone who is trained to listen to you and help you sort out your problems.
You will notice, if you try different readability formulas, that materials rated with SMOG show as being more difficult than the identical texts tested with Flesch-Kincaid. This is because the designer of SMOG based his rating levels on all participants being able to read the text correctly, while Flesch-Kincaid required only 75% of participants to be correct. Consequently, a text that rates at, say, Grade 7 with SMOG will often score lower, maybe even as low as Grade 5, when using Flesch-Kincaid.
By the way, someone who has completed Grade 12 is supposed to be able to read at a Grade 12 level. Remember, though, that in any class, some students will read above and some below grade level. Even for those who can read at Grade 12 level, reading at that level is a stretch. It’s not easy bedtime reading. Most people read comfortably at a level at least two grades below their final year of education. In fact, to reach the general public, written materials should be no more than about Grade 8.
Beyond using standardized readability checks, there is a very important way to find out how easy your materials are to understand: ask real people! This is probably the most necessary part of plain-language writing, certainly for lower-literacy materials. We cannot rely on our own reading skills to tell us whether something is easy or hard. (Which of us writes something we ourselves find too hard to understand?!) Finding appropriate testers is by far the best way to produce good-quality materials for any readership that is different from the writer’s.
Ask colleagues first for constructive feedback (and offer them the same service). Something that looks obvious to you may be totally confusing to someone else because you have skipped a step in an explanation.
Your first, second and third drafts are only the beginning, unless you are the rare exception who is able to imagine a complete document before writing. For the rest of us, only after we have got down what we need to say can we begin to shape our material. Reorder, refocus, and condense or expand as needed. It is easy to wander off topic, as our minds work in interesting ways and can lead us in many directions.
Colleague feedback is only a first step. It is equally important to ask your intended readers what they think, what they understand, and what they like or don’t like. This takes time and costs money, but it is the best way to find out whether your work will succeed, and it will save costs in the long run.