I'm sorry to hear so many people go through such things...
Though I was mostly outgoing, the issue appeared to be that I was seen as uncool/immature since socially I lagged behind. I didn't grasp social cues, I didn't know what the lastest "cool things" to talk about/do were, and to top it off, I liked things that was considered uncool for my age. An example being in my last year of primary school, I didn't care about any of the things girls at that age started to. I didn't realise that hanging out with other losers "pulled down" others' opinion of me, therefore, worsening things. Not that I regret befriending others that were in my position; just outlining what I believe caused the rejection. Also, it's not like I can't understand where the other kids were coming from. Who wants to befriend a 12-year-old with the mental maturity of an 8-year-old? Who wants to befriend the loser and get bullied themselves? While I'll never, ever forgive the bullying, I can understand why most didn't want to associate with me. The others kids had the right to choose whether or not they wanted to hang out with me, of course, but not to bully me.
Towards the end of primary school and before I started my first year of high school, I realised that the "cool girls" liked teen magazines, so I read up on different ones, which lead to me paying attention to other "popular teen stuff" in general. I learned so many things I previously had near-zero idea about- such as celebrities, dating, the latest fashion, make-up, "cool" bands, movies, TV shows, etc. I was heavily associated with the "cool kids" for maybe 3/4 during the first year of high school, but in the end, there were just some "loser" aspects of myself I couldn't/didn't change/hide and I drifted apart from the "cool kids". I became friends with other "losers" and "normals" and though we had our ups and downs, some of use are still good friends even after graduation. I'm glad my more "fake" persona never held out for long, since it would reinforce a worrying belief that being fake is the only way to get ahead and along. I found that popularity wasn't worth the effort. To me (as cliche as this may sound), it was like I hunted for an elusive treasure chest and found it, only to find that it was empty.
When I graduated high school, things started to really look up. I made heaps of friends (acquaintances to actual close friends) though college, uni, work, friends of friends, etc. and most people have a good first impression of me. I've never been isolated or bullied anywhere else ever again. I think it's because of my generally extroverted nature, but also I've learned to become much more socially switched-on because the sad reality is, having even basic (or better, fantastic) social skills is very important. Once I realised That One Nice Person who will be super-patient with my poor social skills and realise what a "good person I am on the inside" is never coming, there were just some things I had to "fine-tune" about myself in order to get my foot in the door and leave a favourable impression. I started off with trying my best to work out what to talk about when and with whom. For example, being aware of the poor (and very ignorant in nature) impression people in general have of "geeky past times". Most people will be put-off by anything perceived as geeky, unless it's particularly popular (such as how it's "OK" to like Studio Ghibli works because "normal people watch them too", Call of Duty since "most cool guys" play it, etc.) or you've gauged that the other person has an interest in those things.
It took a lot thought and effort to work out how to present myself without being fake, but it's worth it since I feel like I can be (mostly, within reason) at the best I can be. Especially because I didn't want to become a doormat or a sycophant.
In short: I was pretty much bullied and/or ostracised to varying degrees of severity throughout my primary and high school years. I've learned to pay attention to what others like which in the process helped me improve my social skills so I was able to "express myself" better and make a few close friends in high school. My social standing became more "don't want anything to do with that total loser" rather than flat-out bullying during the last 2~3 years of school. Unless you're particularly socially awkward, things do look up for most people after high school since you're dealing (mostly) with mature enough people. You can constantly interact with almost whomever you want (rather than the select number of people in your school, therefore, expanding your horizons) and it's much easier to find people with common interests that you can forge genuine friendships with.