Good suggestions - just wanted to add that our 4yo is prone to these rages, and we dealt with the same thing when our 7yo was younger. For both boys, when I tried time-in's, the feeling of being restrained made them freak out even worse, with violent thrashing around, like a caged animal - the last time I tried that, I got head-butted right in the nose. Not fun. So we had to resort to sit-in's with them in a corner, talking to them soothingly and keeping them from hurting anyone or kicking the walls until they calm down enough to be rational. On the other hand, 2yo DD seems to crave the physical contact when she goes into meltdown mode, and holding her helps, even if she fights it at first.
4yo DS had a meltdown going into preschool class last year - they had just fired and awful assistant teacher, and Josh was having anxiety issues with school because of her. So we showed up to find the new assistant teacher there (who, for the record, is SUPER sweet, as is the lead teacher), and DS had a total freak-out when I went to leave. The new teacher tried to hold him on her lap while talking sweetly to him, and I saw him gearing up for "atomic explosion mode" because he felt restrained. So I quickly intervened, and explained his reaction while thanking her for trying. I just sat on the floor with him next to her chair, and loosely put an arm around him and rubbed his back while I tried to distract him by soothingly talking to him about which of his friends were there, what the teacher was saying about their activities for the day, etc. He gradually calmed down and I was able to say goodbye and reassure him I'd see him soon. The teacher was amazed how well my method worked - she said "Wow, you knew just what to do with him!"
What helped us the most was figuring out their triggers! Believe it or not,
diet is a HUGE issue with our kids - meltdowns and rages happen frequently if they stray from their "clean" diet and sneak in anything with gluten, dairy, soy, foods high in salicylates, artificial additives and preservatives, etc. (check out sites like
www.fedupwithfoodadditives.info and
www.salicylatesensitivity.com to see if your DS has symptoms of food intolerances that could be causing these rages.) Sensory processing issues can also play a part - SPD is no joke! If he's craving a certain type of stimulation such as needing to bang on the drums, or getting too much sensory input that he can't handle, that can trigger meltdowns too (7yo has issues with this). Other big triggers for them are anxiety, feelings of inferiority (such as, 7yo is dyslexic and at age 5 started feeling awful about his school work), feeling hurt when they've been corrected on behavior or manners, etc. - of course, these are difficult emotions to deal with even for adults, even harder for kids, and harder still when their whole system feels unbalanced from eating foods their little bodies can't process. Once we figured this out, it became easier to head off rages before they start, reduce how frequently they occur, and lessen the severity when they do happen.
Hope this helps!! Good luck!