Good story. You have a clear understanding of dialogue. I read a lot of stories now days and it seems that people have forgotten that dialogue can propel the story forward. As if to eager to use fancy words wanting to describe every detail instead of letting the reader imagine it for themselves. You found the right balance in description and what to describe. Without even giving a description of the students I can picture them in my head. And I like how you described the plummeting balloon. Two thumps up!