The MP organised the event at Kesteven and Sleaford High School to mark the centenary, and encourage the participation of girls in politics, public speaking and debate.
She thanked the school for hosting it and Chattertons Solicitors for sponsoring the prizes.
A total of 22 students took part from schools across her constituency, split into primary and secondary age groups.
Those joining Dr Johnson on the judging panel included barrister Caroline Haughey QC who prosecutes and defends serious criminal cases as well as prosecuting the first modern slavery case; Liz Graham - head of the family law department at Chattertons solicitors; Lee Rooke - Head of German and PSHE at the High School and Mark Edwards - Editorial Director of Johnston Press Midlands which includes the Sleaford Standard. Each student had three minutes to give an argument on what they would do if they became Prime Minister.
Dr Johnson said: “I was incredibly impressed with the high quality of each student’s speech.”
The first prize was a trip for the winner, a parent and teacher to Westminster, where they will be given a tour of the Houses of Parliament and meet a VIP. The runners up got books signed by Prime Minister Theresa May.
Pupils were judged on presentation, structured argument and reasoned evidence.
The winners were: Primary schools - 1st Nancy Threapleton (Rauceby School), 2nd Layla Grouse (Witham St Hughes Academy), 3rd Hannah Norris (Cranwell School). Secondary schools - 1st Rosa Badham-Moore (St George’s Academy), 2nd Laura Forrester (Kesteven and Sleaford High School), 3rd Rosa Karumazonda (Branston Community Academy).
Dr Johnson said she would like to hold the event again, but next time it would be open to both girls and boys.