Every family and every child is so different, its really a hard question for any one but you to answer but I will tell you my experiences with preschool. My son is a younger school kid meaning he is a July birthday and therefore younger than most of the kids in his class. I put him in preschool when he was 3 (I had this idea in my head I'd have a little free time, HA, by the time I ran him there and dropped him off it was pretty much time to pick him up)Anyways he spent the entire class time running around. I totally thought he was adhd with his behaviour but I talked to quite a few mothers with boys and they all said "He's too young to sit just yet, some kids are at this age some kids are ready for the experience, he so wasn't" SO I ended up pulling him out at CHristmas (this was not an easy decision for me, I felt like somehow we were both failures b.c he wasn't able to do the preschool thing just yet) So I bit the bullet and took him out and I knew within a couple of weeks it was the best decision, he just needed a little more time to be little and be "free" When I enrolled him when he was 4 it was like night and day, a total difference, he participated fully, was attentitive and really enjoyed the whole school experience, a total turn around from the year before. He loved the whole year of preschool and was well prepared for kindergarten with just that one ueay pf preschool (actually I think if I would have forced him to stay in when he wasn't ready it may have had some negative affects long after his preschool days) I now have 3 children almost ready for preschool (my ds just turned 3 in Oct and my twin ds's turned 2 this week) and I have been debating what I am going to do next year. B.c they are older kids (born in the fall and will be older than most of their classmates) it is a different scenario but I think I am just going to go with 1 year of preschool for each of them again. I like the preschool experience mostly for social interaction and since my older ds was an only child for over 5 years that was a big reason why I wanted him to start as soon as possible but I now have 3 within 13 months of each other so I pretty much have my own little preschool right here, they have too much interaction! So I leaning towards the one year of preschool for each of them b.c I simply don't think it is a nessecity.
Good luck
K. H