Parts 1 and 2 in this four-part series of articles (Crossland, 2016, 2017a) discussed the recent research from neuroscience linked to concepts from cognitive development that brought Piaget's theories into the 21st century and showed the most effective provision towards more optimal learning strategies. Part 2 reviewed Demetriou's latest thinking by exploring the relationship between the developing mind and the developing brain for population-sized statistics. Part 3 (Crossland, 2017b) delved into individual differences in development and the implications for schools. This final part makes a case for introducing the teaching of metacognitive skills. [For Part 1, "Optimal Learning in Schools--Theoretical Evidence: Part 1 Piaget's Theoretical Background," see EJ1154880; for Part 2, "Optimal Learning in Schools--Theoretical Evidence: Part 2 Updating Piaget," see EJ1154870; and for Part 3, "Optimal Learning in Schools--Theoretical Evidence: Part 3 Individual Differences," see EJ1154872.]