Hey,
This was done for a challenge, details are below.
Sirius sat next to James as per their usual routine for Potions, with Remus and Peter at the the table behind them. Slughorn was busy writing down the instructions for the day's lesson on the board as the stragglers finished wandering into the room. He turned to face the class as soon as the last person found their seat.
"All right," he called as he noted which students were with whom and where. "Today we'll be working on the Dreamless Sleep potion. Who can tell me what it's most commonly used by?"
At that point Sirius tuned out the professor's voice, instead choosing to randomly doodle on a spare scrap of parchment. James leaned in a few minutes later and nudged him before heading off the the storage cupboard for the required ingredients. Sirius gave a disinterested glance at the board as his friend returned with a couple of extra things, which made them both grin in anticipation.
Ten minutes later Slughorn jumped at the sound of a loud bang. There were several students on the floor near two commonly disobedient Gryffindors who were both grinning like loons. The scattering of Ravenclaws nearby have been drenched in the foul smelling liquid; he finds Lily attempting to put out a mysterious small fire at the other side of the room. Slughorn sent the Ravenclaws to Pomfrey and called the two boys over for a detention after dinner.
Sirius and James' grins grew wider at the news. Remus couldn't help the exasperated sigh at their expressions. "Did you really just do that?"
Hogwarts School challenge forum's Potions assignment 5: explosions, fire