Here are some options you could use, depending on the context:
Formal:
* A group of boys - This is the most straightforward and neutral option.
* A band of boys - This could be used for a group of boys who are involved in some kind of activity or mission.
Informal:
* A gaggle of boys - This suggests a noisy or unruly group.
* A bunch of boys - This is a casual and informal option.
* A pack of boys - This implies a close-knit group, often mischievous.
Specific:
* A troop of boy scouts
* A choir of boys
* A team of boys
Ultimately, the best collective noun depends on the situation and the tone you want to convey.