What can happen to a minor if he she gets caught with half a pound of weed at there house while they are at school First time offense and live in California Clean record?

It depends on exactly what the minor is charged with. Normally under California law, having over 28.5 grams of pot is 0-6 months and a fine of up to $500. The amount you're asking about is way more than 28.5 grams. The minor needs to speak with an attorney who can advise him or her.