The process in which a relatively unspecialized hemocyte precursor cell acquires the specialized features of a lamellocyte. Lamellocytes are a hemocyte lineage that exists only in larvae, but are seldom observed in healthy animals. Lamellocytes differentiate massively in the lymph glands after parasitization and are large flat cells devoted to encapsulation of invaders too large to be phagocytosed by plasmatocytes.