I can see where you are frustrated. I don't blame you. The trampoline was funny and even though it does not bounce, kudos to your son for his creativity (I would have not marked it wrong but deducted points since it wasn't way off).
I do know how you feel. When I was in school the cut off was Dec 31. When my son started school DE had changed their cut off to Aug 30 but we had moved to MD and theirs was still Dec 31 then so even w/ an Oct birthday he was able to start...he was ready but I wish his teacher had been better suited to K so he would have continued to enjoy school. He did fine, typical boy though and a lot like his dad (didn't like school) so he was a lazy student.
I now have a daughter with a December birthday who is academically ready to start school now (she knows everything they want them to know when they come to school and a lot of what they want to teach them during that first year). Is not far off socially right now and thrives at her preschool. She's only 3 right now and therefore wouldn't start school for two more years so I will have her tested this winter to see if she can start before her 5th birthday rather than when she is almost 6. I will honor their professional opinion and do what I have to in order to help her continue to thrive and grow even if they don't let her start early. That said, I know it won't be easy but I will cross that bridge when I get to it.
My point to you is, it sounds like your son is very bright but may need more socialization (not necessarily more as in more or longer days, just more time to grow in that department). Keep doing what you are doing and providing life experiences and plenty of play time (kids learn a lot even though to us it looks like "just play"). Tracing letters helps their fine motor skills (as does drawing, painting, threading pasta or lace boards, play dough). Playing catch helps with hand-eye coordination and dexterity. Museum (kid friendly is best), zoos, aquariums, libraries, parks, nature centers, and other community events can provide a wonderful opportunity to further learning...you can do a different "unit" every month or so. Example: read about going to a zoo, go to the zoo (take pictures and read the info about the animals), talk about what you saw. Then go to the library and check out books about some of the animals you saw (some fiction, some non-fiction). Your son can draw his own picture of the animals (or his favorite animal), make an animal craft or two. Help him make a fact sheet (you write if he can't but let him dictate the info to you). You can do the same with the other venues. Keep it fun...he'll be fine.
Once he does start school, be sure to speak up if he is too bored or too frustated. Speaking up early can make a world of difference.
PS. I went home and asked my daughter what was round and bounces and she replied...a trampoline!