Parts 1 and 2 in this four-part series of articles (Crossland, 2016, 2017) 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. Then the discussion moved onto Demetriou's latest thinking that explored the relationship between the developing mind and the developing brain. Part 3 outlines individual differences in learners with further implications for classroom practice leading to additional characteristics of optimal learning in the classroom. [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 4, ""Optimal Learning in Schools--Theoretical Evidence: Part 4 Metacognition," see EJ1154873.]