This is a major dispute among the authorities; see the words of the Ra'aviah (Megillah, Siman 571), Sefer HaBatim (Kriyas Shema, Sha'ar 2, Siman 7), the Pri Chadash (Siman 58, sub-commentary 7), the Mekor Chaim (ibid., sub-commentary 7), and the Magen Giborim (ibid., sub-commentary 14). Since the Shulchan Aruch (ibid., Paragraph 7) cites a dispute regarding this matter, if one forgot or was under duress, he may read Kriyas Shema after his evening prayers; however, his spiritual reward is certainly only equivalent to one who reads from the Torah generally, as the Vilna Gaon (Gra) wrote (ibid., sub-commentary 17) in accordance with the opinion of those who forbid it.