It really will depend on the breed, maybe see if anyone at the school knows. Cornish x can be butchering weight/size by 6-8 weeks, but even then it depends on how you manage them. If you leave food out 24/7 they will get bigger faster than if you feed at set times, but they may also get too big too fast and could potentially die of complications from that.
Red Rangers and Freedom rangers are second runners up, being butcher size by about 12 weeks.
Something like an Orpington, which can get large, will take 25 weeks to get that size. Of course you could butcher them younger so they are still technically broilers, but they would be rather small and scrawny.
Also, the terms Broiler, Fryer, Roaster, etc really all are actually ages
- Broilers: Chickens 6 to 8 weeks old
- Fryers: Chickens 6 to 8 weeks old
- Roasters: Chickens less than 8 months old
- Stewing Chickens: Chickens (usually hens) over 10 months old
But chickens marketed as broilers generally get larger, like 5lbs + by 6-8 weeks, where most chickens at broiler age are only 2 or so.
Edited by machinfarm - 3/7/16 at 10:08am