Denise Petski Senior Managing EditorEXCLUSIVE: Jason Isaacs (the Harry Potter franchise), Jemima Kirke (Girls) and recording artist-songwriter Dua Saleh will be heading to the classroom for Season 3 of Netflix’s British teen comedy-drama series Sex Education.Isaacs will play Peter Groff, Mr. Groff’s (Alistair Petrie), more successful and not very modest older brother, who Mr.