This is a topic that is interesting because so many people have different approaches to how they set their own personal boundaries.
Like you, Sister Nature, my parents never really explicitly said "Don't talk to boys" it was just assumed and if I ever did say or do anything inappropriate, my mum would just give me "the look" which warned me about impropriety. Growing up, I was terrified of acting improperly cos I knew that if I did, word would get back to my parents on the "auntyji/uncleji"hotline, so I never did.
I was also painfully shy as a teenager, so it was never an issue. It only became one when I married an extrovert who loved to socialise with all manner of people in many different situations (not all of them Islamic) and this really took me out of my comfort zone in terms of interacting with the opposite gender. But even then, I was protected by the fact I was someone's wife - not to mention my hijab and my strict upbringing would never have allowed me to put myself in any uncomfortable situation.
Setting those boundaries, I think is a personal choice. One that each individual needs to be aware of and set for themselves. I've always been conscious of the boundaries, but never more so, than when I went through my Iddah, last year. As much as I wanted to stay home and curl up into a ball and devote my time to self-reflection, I couldn't. I had to work because I was left with debts to pay off and my dad had enough on his plate as it was.
My Imaam instructed me to go to work, maybe pick up groceries if needed and come home. That was it, work/home/grocery store - for three months. But being a teacher and working in a school, you've still got the issue of a lot of interaction with the opposite gender. During that time I was extra conscious of staying out in the open if I had to talk to a male colleague, keeping lengthy discussions on the playground and out in the open, keeping classroom doors open, talking to male students out in the corridor, even though there were glass doors to the classroom.
I am still extra conscious about this especially now since I'm no longer married. For me, its different now, I feel, that being single makes you more vulnerable in the community. It's so vital to protect yourself and set greater boundaries.
It'd be interesting to learn of other people's opinions regarding this.
Please forgive me if I have said anything wrong or improper.