The latest data from the Department for Education shows that 857 of the young people finishing Key Stage Five in schools and colleges in 2016, about 20 per cent of the total, entered the labour market after completing A-levels or similar qualifications.
That compares with 994 a year earlier.
Trade unions put this trend down to job insecurity and the impact of the gig economy among young employees.
Boys are less likely than girls to look for a job immediately after school - 19 per cent compared with 22 per cent.
The rate of young workers for Nottinghamshire is below the average for England, where 22 per cent of the students finishing Key Stage Five got a job for at least six months after leaving school.
Frances O’Grady, TUC general secretary, said that poor working conditions are deterring young people from trying to find a job after school.
She said: “Young people entering the labour market now are more likely to be in insecure work and on low pay.
“A year on from the Taylor review nothing has happened and young workers are paying the price.”
Matthew Taylor, the chief executive of the Royal Society of Arts, published a report a year ago, commissioned by the Government, in which he called for clearer legislation on employment status to adapt employment practices to modern business models, such as the gig economy.
Ms O’Grady added: “The Government should introduce wide-ranging reforms to protect agency workers, many of them youngsters.
“The first priority must be to ensure all agency workers have the same rights to equal pay.”
The most popular choice at the end of school in Nottinghamshire is to carry on studying.
That option was chosen by 62 per cent of the pupils, compared with 68 per cent a year earlier.
A total of 4,285 pupils finished school in Nottinghamshire in the school year 2015-16.
Most of them opted to go to university, with 13 per cent of the pupils going to the 24 leading universities which make up the Russell Group.
The data shows that only eight per cent of Key Stage 5 pupils started apprenticeships after school.
An apprentice will typically spend one day a week studying at a college or training organisation, while spending the rest training on the job under the guidance of experienced employees.