This series was surprisingly good. I was reluctant to watch it at first, cuz it seemed kinda pointless and uninteresting, but I'm really really glad I did. The only reason I rented it was because I loved the themesong so much. LoL. And the themevideo looked decent enuf. Anyways, I wouldn't say that it was super super edge-of-my-seat good, but it was very...pleasant. LoL. I think my only complaint would be that it got a little draggy sometimes (but is overall fast-paced. 30 eps was fine) and it was SO cheesy. I mean, I get the morals they're trying to portray. Don't have to state them out loud...*gag* 
CFO turned Band 3 private secondary school principal via CEO of the company he works for. Just a temporary job switch at first in order to cut expenses at the school, but due to various circumstances, the principal job becomes permanent.
Bobby is so awesome. He's stopped annoying me so much. I really don't know what to say about him. He was at his typical best here.
I really liked his character (as I did most of the characters), but moreso than some others cuz his character had a lot of depth and development to it. He went from an cold-hearted businessman who only cared about numbers to a warm principal who genuinely cared about the school and the students. It was really sweet to see the principal-student relationship develop. (Cheesy, huh? but it wasn't so bad) And I found it hilarious that he always wore a bowtie!! ROFLMAO!!! But I felt so bad for him and his love life. He's so vĩ ðại, but reaps no rewards. 
A good teacher at heart, but it takes some persuasion to make him truly care about the students. Overall, a carefree guy with a happy-go-lucky attitude.
This is the first time I've seen Michael Tao. He wasn't so bad. I didn't think he was too great tho. A little stiff sometimes, but still very funny. 
He had pretty good chemistry with Kenix. I was totally rooting for them! ^_^
I like Michael's character, too. I particularly love his first scenes (and last scene! *sniffle* but I won't give that away ) where he wakes up late for the first day of school and finds out that his uncle took all this stuff and has to run to school with the students. ROFL!!! It's pretty cool how he has such a good rapport with all the students. I wish I had a teacher like that. And when he and the Bobby were opposed to each other. So frickin funny.
Dedicated teacher. Always puts others before herself and doesn't want to hurt anyone.
This is also the first time I've seen Kenix (I know I know! So behind! Don't hurt me! ) Anyways, I loved her performance. She's a pretty darn good actress! Her crying is spectacular. Like when Ah Shan left Miss Wong, I was totally crying with her. And when she was trying to decide between Choi and Leung, I could really see her frustration and confusion.
Kenix is much too skinny. Put on some weight woman! And she looks much better on-screen than she does in photos. Also, the woman cannot dance. Kenix, let's never do that again. lol.
Serious substitute teacher who just got her degree. Bent on being a good teacher and really values her education.
I'm perplexed as to why her picture is included in the cast list. She appeared in less than half of the series. And frankly, I thought her role was a bit unnecessary. The only purpose she served, I felt, was to make Michael serious about teaching. I mean, I can't even remember her name. Anyway, in terms of acting, she's pretty much the same as before: bad. Maybe I just hate her cutesy personality. *shrug* Anyway, she was kinda the turning point of the school. She was the one who initiated the change in the school from uncaring and hopeless to spirited and lively.
Retired sailor who knows just about everything and can fix just about anything. Friendly, warm, receptive guy who really loves his nephew despite the way he's treated by said nephew.
Paul Chun is so AWESOME!!! I loved him so much in this role!! He was PERFECT for it. He was so funny!! That one part where he stepped out of the elevator after the fire. That's one of my fave scenes cuz it was so funny and it was the turning point in Uncle Biu and Choi's relationship. And the scene where he had to switch shirts with Bully! ROFL!! I couldn't stop laughing! Overall, it was a very sweet role and Paul Chun was perfect. 
The students were surprisingly good actors too. I was pretty impressed. They were by no means stellar, but their acting was passable, and that was impressive cuz they are still pretty young and I assume these are their first large roles.
Additional comments:
I liked the school uniforms. They were pretty cute, but how come some of they guys NEVER tucked their shirts in?
How very convenient that Kenix and Michael taught Form 4 one year, and Form 5 the next. But why did they only focus on one class? (I realize that it's more convenient and offers more development, but in the second year, Michael wasn't even teaching the same class anymore) Even the basketball team was all one class!
bottom line: Definitely recommend it.