"Watu wangu getting an E in maths in 1992 haikuwa mbaya kulikuwa na mass failures mean grade ya kuingia campo was C+ and my mean grade was C-," (sic) Sonko twitted on Sunday.
Loosely translates to (My people getting an E in maths in 1992 was not bad there was a mass failure. The mean grade for going to University was C+ and I got C-).
He added "opponent wangu anaeiita 'manager' alikuwa na 4 E's." (sic) It is not clear who he was referring to.
On Friday, Sonko submitted his nomination papers for Nairobi governor after being issued with a certificate of good conduct by the directorate of criminal investigations.
He risked being locked out of the nominations after he accused the party of plotting to lock him out of the nominations.
After obtaining the certificates, Sonko posted them on the social media drawing mixed reactions from users.
In the KCSE certificate, Sonko scored a mean grade of C- with the marks below;
English C-
Kiswahili B-
History and government B-
Geography D plain
Mathematics E
Physical Science D plain
Biological sciences D plain
Social Education and Ethics B-
Agriculture D plain
Commerce D +
"Now I understand why Sonko had faithfully concealed his KCSE certificate, an E in maths. And still he wanna manage the billions in Nairobi? a user, Owinoh Peter posed.
Kamau Muniu said "An E in Maths how's Sonko going to manage 20 Billion city revenue."
"How did Mike Sonko forge a certificate and gave himself an E in maths? Humour galore. Ama he thought E is for Excellence," Smooth Operator said.
Other users told him not to worry that getting an E was not going to dictate his work as the governor of Nairobi.
"A high school grade does not determine one's achievement after school. Go ahead," Abdullahi Yusuf said.
Mgenge said "Sonko usijali... Hawa wasee hawawezi kukushow any."..(these guys cannot tell you anything, go ahead with your ambitions)
"I agree with u, in 90 I got a C+ and went to campus to do business ,I got a D in Maths.I still graduated with a 2nd Upper Class.Resilience," Mzalendo said.
The senator has long been considered the biggest threat to ODM incumbent Governor Evans Kidero.
The August 8 election has seen Nairobi politicians split into two factions.
Team Nairobi is made up of Sonko, Nominated MP Johnson Sakaja, former Starehe MP Margaret Wanjiru and Dennis Waweru of Dagoretti South.
The team's talks on the best candidate to face governor aspirant Peter Kenneth have hit a snag.
Kenneth, who is from Murang'a county, is in the other team with Nominated Senator Beatrice Elachi and MPs Rachel Shebesh (woman representative), Maina Kamanda (Starehe) and James Gakuya (Embakasi North).