After playing at least one level in play mode, select ‘Coach’ from the game modes in solo. You can only coach yourself on minigames you’ve unlocked through play mode, and you have to start at bronze and work your way up to gold. Select a category, then a minigame from the list and answer each question correctly for all 3 difficulty levels and this achievement is yours! In order to get each medal you must answer all 10 questions for that difficulty correctly. If the timer runs out, it counts as a failed question, so you'll need to start that particular difficulty level again if this happens.