Bella's stepdad is retired, so he's usually able to stay at home with Jango while she is at school. The other day, however, he had a doctor's appointment, which meant the lizard would be left all by his lonesome for a while.
When Bella learned of this, she decided to act. Without anyone noticing, that morning Bella loaded her backpack up with a pillow, blanket and some food — and then placed Jango inside. She then snuck him to school so he wouldn't have to be sad by himself at home.
The pair got to hang out together for most of the day, until fifth period when, their adorable plot was uncovered by Bella's teacher.