Transcript for This school's main entrance requirement is students must be addicts: Part 1
week of not getting kicked out, not dying. If I can do that for like five days. Reporter: For Harry, staying alive is a goal you have to set. . I feel like such a scumbag. I'm Harrison. I am an intravenous heroin user. I'm going to get high. I don't want to use, I just can't stop, you know? You got to stop recording. I'm Nicole. Been doing drugs since I was like 13. I always felt like lonely and depressed. And anxious. Other than that, I never felt anything. When I say to her things like, you should be a model, she looks at me like I'm crazy. It's a struggle. My name is Matt. Instantly I did a line of oxy. And I fell in love. And it ruined my life. Reporter: Harry, Matt, and Nicole are all students at an experimental public high school in Worcester, Massachusetts, with one main entrance requirement -- you have to be an addict to get in. The first thing I think of when I wake up is just like, how's today going to go? Am I going to use today? I love them like my own children. I don't want to give up on a single kid. Reporter: Susan strong is the principal of rockdale recovery high. I'm afraid they're going to overdose. Overdose and die. That's my greatest fear. Okay, what have we got here? Midge call urine? Reporter: To remain a student you have to be clean of all drugs and alcohol. Look how clean that is! Reporter: As America's opioid crisis balloons and teenagers become addicted at younger and younger ages, many people hope this model could be an answer. Grant me the serenity to accept the things I cannot change -- Reporter: "Nightline" spent an entire year documenting these students' struggle for sobriety. Did everyone hear what we're doing? We are making cards for Carrie. Is she coming back? Reporter: They're starting off this school year without Harry. Harry relapsed and almost died on December 26th of 2015. It took two shots of narcan to revive him. Har Harry's at a halfway who is in Springfield. He's kept us away so many night records we love him, we want him back. Reporter: Clean from heroin nearly 90 days, he is free to leave for the day to visit recovery high. My heart's beating a little fast now, I must say. You look fabulous. Harry! What's up, buddy? How are you doing? Come in it will be like old times. It's bittersweet because we've had these moments with Harry where he's come back and has been in treatment. Don't act like you don't see me, bro. Without notice the very next week Harry could be on the street carrying 20 bags of heroin. Reporter: At the end of the day, Harry heads back to his halfway house with hopes of rejoining his classmates full-time soon. I did some pretty crazy things to get drugs. I stole money. I sold myself. How bad did your addiction get at its worst? At its worst? I end up watching my friend pass away from an overdose, and I felt responsible, because I was the one that they used the narcan on last time so I was the reason there was no more narcan. You had od'd in that same space and they used narcan on you, so there was none left? Yeah. I've been pretty depressed lately. Just been going through whatever I've been going through. Reporter: After school, instead of going home to her family, Nicole spends her evenings here. This is a shared apartment between every lovely person that lives here. One day there was like 15 of us. This is our home. Her parents even knew that. She's disconnecting from her family, I worry about that. She is like a mother to me. Reporter: L.J., a former heroin addict herself, knows how precarious sobriety can be. That's why she says she's always prepared. Narcan because you never know when people will overdose or relapse and stuff, you want to be prepared. You take the cap off and put it into the nasal, stop somebody from dying. I almost died. Doctors say I would have waited a couple more minutes, I'd be brain dead. There's a batch of heroin people od and are dying on. In the thick of our disease, we don't care. We're going to go for the stuff that's taking everybody out, because that's the better high. It's Friday morning. Woke up about 30 minutes ago. This thing could go . Reporter: Matt stopped using oxycontin just two months ago. Mostly what I was escaping from is I didn't feel I belonged, I didn't feel like I fit in. Reporter: He's now trying to find his footing in sobriety. I hurt a lot of people. I remember telling my dad, burstiburst ING into tears when I told him, it hurt him so bad. Reporter: To help him, Susan tries to find a hook. Something to distract him from the urge to use. Susan is hoping that hook is hockey. I'm out there, it's like a natural high. Oh, yeah, right! Reporter: Matt's father, who lives in another town, comes to watch him play. He took to it. It's so awesome that Matt's dad came today. That's a relationship that's really important to Matt. It's my favorite thing to do is this. Play hockey. I don't know, why it's just really fun. See you later. Reporter: As we near the end of December, Matt and all the students are dreading the holidays. Because it's going into the holidays. Holidays are usually the worst in recovery. I don't know, it's just really stressful to have the whole family together. Stressful. Aunty Susie always making drama. Usually everyone's drinking. Reporter: For Harry, this time is especially dangerous. He has decided to leave his halfway house. Living back at home now. I don't get that much money at a time, so I don't get high. Hi, Harry. Hey! Whenever Harry goes back, he immediately starts using heroin. And for Harry, that's a death sentence. Reporter: Fearful that Harry is using again, Susan asks him to come visit. Hey, what's happening? Reporter: When she sees him, her worst fears are confirmed. You look pretty high right now. Oh my god -- yeah I've done a per. Have you shot heroin yet? No. That's a one-way road for you. Because you almost died. We might not be so lucky to have two shots of narcan to bring Harry back to us. Yeah, I feel that. Yeah, so that's what's killing me. That's what's killing Alisa. We don't want it to happen again. Let us get you someplace where you're going to be safe. Harry doesn't think he's worth saving. And I can't -- you can't walk away from that. What's this like for you? We can't convince Harry to care about himself and believe that in ten years he's going to be amazing. Because he will be. If he's not dead. Reporter: Unable to get Harry to go back to rehab, Susan reverts to plan "B." Sweetie, you can walk in here tomorrow and start school. Yeah? Yeah. You can't come high. No . Will you show up tomorrow? I probably will. We would like you to. Hopefully any minute he'll be in. Texted him this morning, just checking to see if he's still coming in -- Fingers crossed. Oh, here he is. . Nice to see you too. Thanks for coming in. Reporter: For Matt, the shock of seeing Harry back in school quickly gives way to the realization that Harry has relapsed. That's my choice to leave? No, not at all. What are you using? Percs again. Dude, you're going to die. . Really makes me sad about Harry. Because I'm good friends with him. You know, he will die. 100%. I know it. And it's going to Suck. Reporter: The next day, Harry is a no-show. Hi, deb, I wanted to check in. Reporter: Susan calls Harry's mom who informs her that he won't be coming in today. He's staying home to help work? For real? Yeah. I have to think that is an awful decision. Awful decision. He needs to be here. It's the worst decision on the planet. Reporter: Without being connected to his sober friends and without the close monitoring he gets at the school, they are convinced he will use heroin. I'm like -- are you freaking kidding me? I got nothing. So angry. You know what we're going to do? Focus on the kids that are here. And be positive. Because they deserve our attention. Reporter: As the day ends and school closes down for vacation, the other students cope with holiday stress by exchanging one addiction for another. We're going to save some money. We're going to buy things we don't need. Stuff we don't need. It's awesome being able to go to a store and actually be able to buy stuff. Cause I used to spend all my money on drugs. Reporter: Harry is coping less well. December 27th, 2016. A year ago yesterday, I actual actually -- when is I overdosed. Sadly, I haven't stayed clean. Been getting high every day. They don't really know that. Reporter: Then he drops a bomb on us. We are driving to go get high right now. Yesterday and today I've Gott gotten -- I got high on dope. Reporter: He is back to using heroin. Hey. Got to stop at a corner. We just grabbed from a guy I knew. Bag of dope. We got to turn off these lights now. Reporter: In that car, Harry is using heroin. The thing that nearly killed him a year ago.
This transcript has been automatically generated and may not be 100% accurate.