Adult attentiveness is THE miracle elixir in all education of a young 'un. You can be your child’s supreme example of it. It is what Leonardo Da Vinci's uncle used with him, while his own dad (a rounder and a playboy) ignored him. SOME adult, somewhere, who is watching, listening, can be continually adding beneficial stimulation and exposure. Some parents nowadays seem to have no ability, proclivity and/or interest and time in giving it to the next generation. They don't even understand it. Don't know it exists. Didn't receive it themselves. Therefore, for the child's sake, the adult who CAN do so must do what is possible to engage each child in some sort of progressive curriculum, even if it is only to talk them through it all.
Simple little workbooks, loaded with lovely and exciting color (I despise and eschew poor artwork or movie artwork passed off on children) add up for step-by-step progress as a track to ride. This helps immensely for the average parent of a young child. You may be able to add surprises (for example, “Let's read this page backwards”) and silly songs, and loads of whimsey, stories, drawings, etc., to drag them through the print. For an older child, you might say “Just read this section and summarize it for me,” or, “Tell it to your brother or your grandma,” or “Tell it to the tape recorder or the car in the garage,” instead of subjecting the child to endless filling in of blanks of a workbook...but reading of it yes...so workbooks can be used for a long time, if the RESPONSE pattern is EZPZ and differing. You’ll be only using the text for the exposure and stimulation, whether it is from a textbook, workbook, or good quality readings of well-written books. Some states’ homeschooling laws require standardized tests be done every other year...3rd, 5th, etc. so that is on the parent to make sure that they have some mastery of the basics. Grandparents should not be responsible for that overarching load. They get to merrily focus only upon enriching the child.