Some days are just more challenging than others with kids...

So I'll start off with saying that my three kids are awesome, but some days they are more challenging and perplexing than they are cute and funny.  This was one of those days with my second son, Andre.  A bit of background, Andre has had some behavior problems ever since he was about 13 months old.  At first he would throw little hissy fits when he couldn't make out words, or was trying to show us what he wanted and we didn't understand.  He only said "mama" and "dada" at that point, but it seemed like he was trying to get a few more words out.  By the time he was 18 months, he had stopped saying "mama" and "dada" and had no other words in his vocabulary.  He wasn't really trying to point to what he wanted to "show" us what he needed, instead he would throw full blown tantrums for no reason what-so-ever and would hit/kick/bite other children and adults around him.  It was so bad we didn't go out to eat anymore and had severely restricted how much we would take Andre to play with other kids for fear that he would hurt them.  Our doctor had us get Andre tested for a speech delay, and we found out that at 18 months he had the speech development of a 9-12 month old.  We started with a speech therapist who came to the house, and began seeing progress after about 6 months of therapy, and now we have him with a new speech therapist at the public school system that he sees about once a week.  Compared to where he was, Andre is leaps and bounds above the speech level he started out as.  He is now three, is speaking in small sentences, and even when he doesn't talk he tries to communicate in some way what he wants and needs.  The biggest problem that we still have is that he still will, for no reason, hit/kick/bite other kids if they dare to touch anything he wants to play with (or doesn't want to play with) or if they don't bend to his will right away.  When he is with us and starts this behavior (depending if we are at home or out in public) we will remove him from the situation and either take him home (out in public) or put him in his room until he calms down (at home).  At daycare they do the same thing, and yet we still don't see any results in Andre acting any differently.  I feel at my wits end, because I don't know what else to do, and he won't quit this really mean behavior.  I have tried spanking him a few times when I was horribly frustrated, but I think this makes him think that hitting is ok, and I don't want to confuse him, so I stopped spanking him to try to get the point across.  At preschool we are going to try to start not allowing him to go back to preschool the next visit (he only goes three times a week-they don't have a five day a week program) if he acts up and hurts the other kids in his class. Hopefully we will be able to curb his behavior this way because if not I'm afraid we will have to pull him out of preschool all together.  I'm really hoping he stops behaving like this (with my oldest I never had to worry about this because he always wants to hug/kiss and take care of every kid around him), because if he doesn't I just won't know what else to do.  I just hate days like this because it makes me feel like I'm doing nothing right.  Ugh, hopefully tomorrow will be better....