Full training does not change as your Tamagotchi grows older. If you have all of your training bars, your character is less likely to call for attention when not required and probably less likely to start crying all of a sudden. If you aren't sure how to get training bars, here's how to:
1. Give your character a time out if it calls for attention and every heart is full
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2. Praise your character if it starts crying all of a sudden and it's hearts are full.
Hope that helped!