I used to teach middle school, and we were constantly giving out food as treats. It still bothers me to this day. And I tried to give out other things (stickers, pencils, bouncy balls, etc), but they didn't go over as well because everyone else was handing out candy.
At the end of each grading period, students were given a "Positive Perk" if they had no referrals for that grading period. They were handed out in homeroom, and then redeemed at lunch for a can of soda.
Students could earn "cool tool tickets" on a daily basis from a teacher for just doing the right thing. If I saw a student pick up a piece of trash and throw it away, I could give them a cool tool. I was encouraged to stand in the hallway with a stack of them during my hall duty and hand them out freely. They were redeemed at lunch for a piece of candy, and twice a week they were drawn raffle style for a spin on the wheel. The prizes were a little better - GC's, small toys, bag of microwave popcorn, etc.
And for a bigger job done, I could hand out a certificate (can't remember what they were called) when a student went beyond their normal responsibilities. They were redeemed once a week at lunch for an ice cream sandwich.
And that was just the tip of the iceberg in terms of all the other candy handed out on the sly, or just because. The band teacher used to stand at the door with a bucket of candy for the students who brought their instruments home over the weekend.
It got really frustrating - but while I was frustrated by it, it was a system that I had to buy into. I think that if you (as a parent) are frustrated, start brainstorming with a teacher who you know and trust. They might have a few different ideas of rewards/treats that don't involve candy. That teacher can talk with other teachers (who might be as equally tired of the candy), and then start bringing change forward. I think this is a topic that needs to be handled from the bottom (the teachers), and then they can present a concrete idea to the top.

(I used to eat a lot of it myself, too.

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