mom of a "shy" 3.5 yr old here. i'll relate my experience and you can see what might resonate with you. dd1 was very shy even as a baby. we have not moved and have been involved in the same playgroup since she was about 5 mo old. she has never really played a whole lot with other kids, though. i think she just has a very cautious temperament. she hates people getting in her face or taking her stuff and y'know that's what a lot of little kids do. i've been reading "kids, parents, and power struggles" by kurcinka recently (highly recommend it) and she talks a lot about temperament in there. some folks just take longer to warm up than others. my dd1 is definitely one of those, but now she's starting to really open up.
we're taking a dance class this fall (moms stay and watch) and she loves it. she had developed the common 3 yr old girl ballerina obsession prior to class so it was an easy classs to decide to take. i guess we've been to 5 or so classes now and dd1 is really starting to participate. she was always dancing before, but was on the fringes and not joining in the circle, etc. last class she still did her own thing, but really listened to the teacher and followed instructions more than ever before. she even joined in the circle a time or two.
i think preschool would have been a disaster for us. maybe next year. dd1 is also _very_ oppositional. i have a post elsewhere (http://www.mothering.com/discussions...d.php?t=198122
) where i mention a typical encounter with a well meaning person in the grocery store:
clerk: that's a very pretty dress
dd1: it's NOT a pretty dress!
clerk: what's your name?
dd1: i don't have a name!
this happens almost every time we're out. there have been a few tims recently where she's struck up a conversation with someone though not usually if they point out her dress orsomething. i can see glimmers, though, of her growing out of some of the opposition and defiance and shyness, too.
if you want my advice i would say do not push anything anymore than you would push her to walk or potty train or sleep through the night by herself. just be there for her and support her and when she's ready she'll let you know.