J.B.
Def provide a snack to the kids if dinner is late. If it doesn't help, hire a babysitter for your youngest and oldest child and spend some alone time with your middle son. But, do not present this mommy-child one-on-one time as a reward to your son for his poor behavior as this could reinforce the behavior. Rather, try to spend one-on-one time with all your children, use that time to run necessary errands you have with your son (does he need clothes? shoes? school supplies?). Try to get him to talk about his feelings while you are alone with him. Perhaps he will tell you he is he having difficulty at school, misses his father, etc. If nothing is forthcoming, ask him why he has been melting down in the evenings.