At Buruburu Girls' Secondary School on Saturday, he said there was no need to panic ahead of the national test that will begin in October.
Sonko told the students to focus on their studies and ask God for courage to write the examinations.
"Never lose hope in life. In my days in school I was very naughty and did not do well in my exams. I got a C plus with a clean E in Mathematics but here I am. My courage to face the challenges of life has put me where I am today," he said.
"You might have scored low grades in your lower classes but don't let that define who you are. Focus and dedicate some time to God. He will give you the courage."
He went to the school to give an inspirational talk and launch a laboratory, library and swimming pool.
The Governor attributed his success to his late father Mzee Kivanguli whom he praised for teaching him life skills at an early age.
“I salute my late father. May his soul rest in eternal peace. He taught me a lot,” he said.
Sonko told the girls that he made his first one million shillings while still in high school, an accomplishment that he said showed he had entrepreneurship skills.
Land was very cheap back then, he said, adding he saw and took opportunities that others did not.
“Omar Mwasabuni in Diani was one of the first people who sold land to me. I sold it to a German national and made good cash,” the county chief said.
“You must strive to achieve anything. Life is not as easy as it might seem. You should also always put God ahead of everything," he told the girls.
“Don’t think of your family background or what you ate last evening. Just focus on your life path. You are the future of this great country of ours."
Sonko said he had seen God's hand in his political life despite many hurdles.
Since his first campaign as Makadara MP, he told the students, he had his accounts frozen and some of his clubs closed but he kept trying to succeed.
Sonko has been troubled since taking office as Governor in August - key issues are the garbage collection, hawkers and matatu menaces.
The city is in shambles but he says he is doing his best and that cartels are getting in the way.
On June 8, he hailed President Uhuru Kenyatta's tough measures to rid the country of corruption and asked investigative agencies to go after cartels that he says undermine his administration.
Source: The Star