Recent posts I've seen in the forum suggest that Google haven't updated PR since April, which would explain why your site hasn't been ranked yet if it's only six months old...
Whilst Google's internal PR changes all the time and is based on many factors, the PR you see in a PR Checker/Google Toolbar is rarely updated, is calculated entirely based on inbound links, and is compiled of old data even when it is.
Seriously, it isn't worth worrying about. As you say, your website seems to be attracting visitors, so I'd suggest you concentrate on making the site the best possible resource it can be for them, and worry less about PR...
-------------------------
Teacher Licensure Colorado