The only answer keys for the Avancemos 2 workbooks sold by Houghton Mifflin Harcourt are the Teacher's editions, as of 2015. However, a user may be required to have an institutional account with Houghton Mifflin Harcourt to purchase the teacher's edition.
The Avancemos series has a plethora of learning tools available to users online through ClassZone. This site has a home tutor program complete with games and animations to help students with difficult sections of the book. ClassZone also provides flashcards and self-check quizzes for each section to help students learn from home. It even provides downloadable audio and video files to help students practice the pronunciation of words.