Admittedly, I was pretty lazy in my teenage years. Going to university and finally being on my own for a change put an end to that.
Not that university is a motivator for everyone. I had a roommate who regularly missed class because he was too busy sleeping until 3pm, or browsing the web, or playing his Wii. His academic adviser actually contacted me and the other roommates a few times, always pleading for us to get him to go to class before he failed everything (this was our second semester of senior year too). He ended up not graduating with us and letting his parents foot the bill for another year at the school... all because he didn't feel like going to class...
Not that university is a motivator for everyone. I had a roommate who regularly missed class because he was too busy sleeping until 3pm, or browsing the web, or playing his Wii. His academic adviser actually contacted me and the other roommates a few times, always pleading for us to get him to go to class before he failed everything (this was our second semester of senior year too). He ended up not graduating with us and letting his parents foot the bill for another year at the school... all because he didn't feel like going to class...