For 10 years now, Hoang Trong Khanh has been providing free lessons for dozens of poor children every night after work. 

Khanh, 39, has been organizing free classes in a 30-square-meter room in District 9, mostly for workers' children.

Each class has around 50 students, from 6th to 9th grades. Khanh has classes every night from 5:30 p.m. to 9 p.m., divided into two shifts. He teaches math, physics, chemistry, literature and English.

Teaching is not Khanh's full time job. He is an employee of a pharmaceutical firm that makes veterinary medicine. For most of his classes, he does not even have time to change from his office attire. 

"When I first came to this neighborhood, I saw the children, faces were smudged with dirt, diligently read books even without supervision. They looked lovely, but it was still sad. I was afraid they would quit studying because of poverty, so I decided to teach them for free." 

When he first opened his classes, there were only a few students. They studied in a shed on an empty plot of land, before locals helped build a temporary house for the classes. For the last three years, Khanh has managed to rent a full-fledged house, both as a place of residence and a place to teach. The landlord, impressed with Khanh's good intentions, decided to let him rent the place for just VND3 million ($130) a month.

Ngoc Phuong, a 9th grader, has been studying in Khanh's classes for three years. Her father is a manual laborer and her mother lost her ability to work a while back.

"Teachers used to say often that I understood my lessons more slowly than my classmates. Since I have started taking Khanh's classes, I have become better. It's easy to understand what he teaches, so I have managed to get an “excellent student” citation for three years straight," she said.

Khanh buys on his own the chairs, tables, pens, board and other things needed to teach. Even though he can’t access modern equipment like projectors, he tries to illustrate his lessons using images and videos on his phone.

As someone who only finished high school, Khanh didn't have a formal education training at first. He later sought the assistance of other teachers to learn how to teach and enrich his own knowledge.

"The most difficult subject is English because I'm not good at it. As I already have the foundation for other subjects, I can continue to learn them on my own and teach my students according to the education ministry's curriculum." 

Khanh instructs a boy on how to sit with the right posture during a physics class.

Khanh high-fives a student. 

He said he tries to maintain an upbeat and happy atmosphere in class to erase any gap between him and his students. The children fondly call him "uncle." Khanh said he uses humor and practical examples to help his students understand the subjects better.

When 12-year-old Nguyen Hoang Tan Khang ran out of notebooks, Khanh gave him 10 for free. Other students have been provided school supplies for free if they ran out of stuffs.

Khang is one of many whose parents are also workers in the same company as Khanh's. They happily send their children to Khanh's every night for studying.

Khanh also buys snacks and other food for his students once a month from his own pocket, as rewards for their study.

On September 21, he bought around 30 bubble tea cups for his students before class.

When the students return home at around 9:15 p.m., Khanh would stay back to look over other lesson plans and grade his students' tests. He's still single and does not have a family as his "love luck hasn't come."

During the day, Khanh works at a veterinarian pharmaceutical firm, about two kilometers away from his apartment. He has been working there for the last decade, ever since the day he moved to Saigon.

In his free time, he takes care of chickens that he breeds in the basement of the apartment. 

He earns around VND6 million ($258) a month to make ends meet and maintain his classes.

But Khanh is not complaining. "I'm single so whatever's fine. I just hope that the children study to the fullest, make progress every day and become good public citizens, serving society. That by itself would make me happy."