As head of a secondary vocational school, Zhang Juncheng does not avoid to tell his students that he used to be a security guard when he was a young man.
The 41-year-old from Changzhi, North China's Shanxi province, believes a person's position in society is not decided by others, but their own efforts.
Back in 1995, Zhang, who had just graduated from a junior middle school in Changzhi, tried different jobs before being hired as a security guard at Peking University.
Standing at the gate of the prestigious university, Zhang was content at first.
"I was ignorant then," recalled the man.
He only changed his mind after he read a story from an ancient book. The story is about the cart driver for Yan Ying, a famous politician from the State of Qi in the Spring and Autumn Period (770-476 BC). The car driver was arrogant because he worked for such a big name like Yan.
One day when the driver returned home, his wife told him she wanted a divorce. The woman said her husband was so arrogant whereas Yan Ying, a high-ranking official, was modest. The driver then realised his shortcoming and became a modest person.
Another thing also left a deep impression on Zhang's mind. One day on duty, he saw an elderly man riding a bicycle towards the gate. When the man went by him, he nodded and said to Zhang "Thanks for your hard work."
Zhang did not expect such a respect from the man and was amazed to later find out that the man was the president of the school.
At Peking University, Zhang embarked on his road of learning thanks to the help from several teachers.
Zhang Yushu, a foreign language professor, liked talking about philosophy with the young security guard and recommended lots of good books.
Another professor called Zhang Xuecheng encouraged him to read more and "make a plan for his life".
Under the guidance of teachers like them, Zhang started reading diligently. He liked reading literary, philosophy and history books. When he got off work, he read books, transcribed books, and wrote a diary. When the dormitory's lights went out, he continued to read by torchlight under his quilt.
The head of the security guard team later extended the time of lighting in the meeting room so that Zhang and several other co-workers could read at night.
Another incident at the university struck Zhang.
One day, Zhang blocked seven foreign students from entering campus because they didn't have the right ID cards. Not knowing each other's language, both parties refused to give in. Later, the foreign students left, gesturing to Zhang thumbs-down to show their anger.
Upset at the way things had gone, Zhang reflected on the incident, determining that it was because he did not understand English that the incident had got ugly. So, he started teaching himself the language.
He used his spare time on duty to read and his efforts were spotted by Cao Yan, an English professor at the school. The teacher gave him permits for English class and encouraged him to sit for the national college entrance exam for adults.
Moved by the good intentions of the teacher, Zhang started attending English class. He shuttled between the classroom and the sentry box every day. He left his post 10 minutes earlier than scheduled to change the uniform as he "felt a bit inferior wearing the security guard uniform in the classroom."
In the autumn of 1995, Zhang attended the national college entrance examination for adults and was enrolled in the law department of Peking University.
As a security guard-turned college student, Zhang shot to fame in the school and was invited to lecture other students.
Zhang said over the past two decades, he has kept doing two things: keeping a diary and getting up early in the morning.
He said he keeps a diary and reading notes, habits he developed as a university student. Even after rising to school headmaster, Zhang gets up at about 6 am everyday to go to the school's playground.
Zhang's story has inspired more people to change their lives. According to media reports, more than 500 security guards at Peking University alone had passed the test of the national college entrance examination for adults, with some even obtaining master's degrees.
After graduating from the university in 1998, Zhang returned to his hometown and worked at several vocational schools, before he establishing a secondary vocational school in 2015 along with four friends.Zhang introduced a military-style management in the school because many of the students used to be poor in academic study and indulged in bad habits such as smoking, drinking and fighting. The system is designed to correct their bad behaviours.
Speaking about his reasons for working in vocational education, Zhang said: "At 15 or 16, kids who graduate from junior middle school are too young to enter society and should continue their study. With their mental conditions not yet shaped, they are prone to bad habits."
He intends to build his vocational school into an exemplary one in the city in the short term, and also aims to build the first privately-run university in Changzhi within a decade.