Wow, great start! You managed to pack so much into this one chapter. I loved seeing your version of the Occlumency lessons, the potions class, ect. I also really liked the side plot with Draco, that Draco needs help. I feel that you did a good job delving into his backstory without loosing your readers. It added to the story. Snape seemed like he swiitched from violent to caring too easily, you need to build that part of his character up a little bit more to make him seem more realistic as a character.

My main thing is that I wish you'd work on and fix is some of the writing. You switch tenses, especially in the first part of this chapter. You can't do that, the narration needs to be in one tense. You got better as the chapter went on, so it's probably just a beginning thing. Also, when you do dialouge, you can't really start a new paragraph with the same person speaking, the reader will automatically think that it is a new person speaking. The only way you can make a new paragraph is if the person's speak goes for more than a paragraph and you don't add the end quotes before moving on into the next paragraph, like so:

Snape slowly shook his head,"You don't know do you? ...ect... What you did was wrong.

"I don't know what else to tell Dumbledore... ect..."

Please go back and edit this chapter. I think that your tense problems and little punctuation things and the formatting is making you loose readers. They start the first chapter but don't want to keep going because the writing constantly jars them from the story and then they can't enjoy it. I'm going to now post some things from your writing so you notice a couple of what I'm talking about:

Snape sighing in frustration, "Don’t worry I won’t harm a hair on golden boys head." (your golden boy's head?)

A surge of anger shot through Harry, how dare Snape make him relive Sirius’s death, how dare he restrained him. (restrain?)

"Potter, get back to your seat." Snape commanded sternly. (...to you seat," Snape... You need to use a , not a . here.)

Draco pulling his arm out of Snape’s grasp, tore out of the room. Snape letting him go. Numbly Snape collapsed into his chair, his eyes closing. (Draco pulled his arm... or, Pulling his arm from Snape's grasp, Draco tore out of the room. Snape let him go. Numbly, Snape collapsed into his chair and closed his eyes.)

by samhaincatA Soul at the Edge of the Abyss (I odn't think you meant this to be in the middle of your story text. It's right above the last horizontal rule (line ----- thing). I took it out for you.)

"What do you care," sprinted through Harry’s mind. However he followed Snape’s instructions, not wanting a repeat of the last lesson even more than Snape. Once was humiliating enough.

(You have a double post here of text. I'm going to take the second one out for you.)

because you didn’t go to Sirius and keep him at Grimauldi place because…" (Grimwald?)

"Potty what’s up with you? Is there a Dementor on your tail?" Malfoy snarled viciously.

He pulled out his wand "Because of you my father is in Azkaban it’s time you paid for that!" He lifted his wand and pointed it just as Harry tried to grab for his wand. (Put these two things from Malfoy on the same line or I'll think Harry's the one pulling out his wand.)

Crabbe and Goyle backed away and left the room in a hurry.

"Cowards," sniffed Draco. 

 Great start, update soon.