I have not seen that post. I've heard that kids often don't read until about 6/7, and that is perfectly normal and not a sign of a delay. Indeed, many countries' school systems don't start formal reading instruction until kids are 6/7, at which point most learn quickly. But by third grade, when most kids are 7/8, not being able to read at or near grade level will be a serious handicap. In third grade, kids are no longer receiving formal reading instruction, but are instead learning grammar and spelling, and working on writing sentences with capital letters and appropriate punctuation, plus learning about different kinds of writing (narrative, opinion, factual reports) and doing social studies and science based, in part, on reading from various kinds of texts. They are doing word problems in math. A kid who can't read by third grade is really going to struggle.