Hi Christina @Jojojazz89I can understand your frustration, and I can also understand your 12 / 13 year old son’s “need” for a snack. I’m not a parent of a child or grandchild with diabetes, thankfully, but I myself with seven decades living with diabetes very safely will snack late evenings; the milk or juice only is included in snacks when I am “trending low” - I really hate being awakened by night-time hypoglycemia.
Discipline appears to be ineffective in this particular situation for you, so why not try “education”? At your son’s age, he is quite capable of understanding the basic formula about balancing food and activity with insulin - he knows well by now that the required insulin is not being produced by his body, so he needs to inject. Help him implant in his head that FOOD = INJECTION, and see that he follows this rule - unless he is already “low” or involved in certain activities.
Have him write down the carbohydrate counts for snacks he likes and would take in the evening. Also write down specific Insulin:Carbohydrate ratios for times of day and even to make things more simple, keep a chard handy with customary snacks and insulin required for his glucose level - yes, require him to do a finger-stick - OUCH factor. By 7th grade he HAS the arithmetic skills to do these calculations in his head.
Please try to avoid making eating a crime - from my experience, greatest character talent developed the required starvation-diets for managing diabetes in the 1940’s, 1950’s, 1960’s was the ability to lie and cheat when eating.