Most children, even very bright ones, need constant review and practice to truly own a concept in grammar, math or science. In schools today, on paper it may appear that kids are learning skills, but in reality they are only renting them, soon to forget what they've learned over the weekend or summer vacation.
Rafe Esquith (2009). “Lighting Their Fires: How Parents and Teachers Can Raise Extraordinary Kids in a Mixed-up, Muddled-up, Shook-up World”, p.22, Penguin
