Did you know that Google now is able to estimate the reading level of a page, it does this using a number of well established formulae that were developed in the 19th and 20th Century by mathematicians studying language usage, these count up the number of words and then look at the ratio of verbs to nouns to pro-nouns etc.
There are clear mathematical differences between the way that primary school children and research scientists write and this can be measured using the above approach. In general Google rates pages with a higher reading level as of better quality, but it all depends on the search phrase. So a search for “Childrens stories” would be best served by Basic level, whilst a search for Quantum mechanics topics an advanced level.
Its important to understand that Google works in this way and you need to work through your entire site making sure all your text is fit for purpose and matches Google’s expectations.