I have used this activity with 6th, 7th, 8th grade level students, as well as reading intervention (remediation) students. Not only does this activity lower the affective filter, it really breaks down the walls of defensive or unmotivated students.
I've also played a variation of this game at the end of the year. The snowball prompts were different (e.g. what was your favorite part of the school year, what was your favorite unit, advice for next year's students, etc). Kids enjoyed seeing how they had come full circle
This download include originals for the snowball activity and teacher directions.I have left this document unlocked, so you can tweak it to your liking.
Enjoy! Happy snowball fight!