It means the constituency has one of the highest average class sizes in England. It has risen very slightly since 2010-11, when the average class was 24 students exactly.
Meanwhile the average primary class size in the area is 27.5 students, which has also risen by 0.1 pupils over the same nine year period.
In Telford, the average secondary class size is 19.4, making them the smallest in Shropshire. The class size there has actually fallen over the last nine years by 0.2 pupils, the only Shropshire constituency that saw a reduction in size.
The average secondary class size in the Wrekin constituency is 21.8, a rise of 0.1 on 2010-11.
In North Shropshire the average is 20.6, a small rise of 0.1.
In the Ludlow constituency, which includes much of south Shropshire and Bridgnorth, the average class size is 22. That represents a rise of 1.1 in the last nine years.
Shrewsbury and Atcham is one of the 20 English constituencies with the largest average secondary classes.
They also include Nuneaton, Stockport and Harlow. All 20 have an average class size of 23.8 or more.
A union official today said that cost-cutting Government policies have "put a squeeze" on schools.
The figures, analysed by the National Education Union (NEU), said that Shrewsbury and Atcham has a total of 4,212 secondary students.
Nationally, the NEU said that teaching assistant numbers in secondary schools have fallen by three per cent in the last year and by more than 15 per cent in the last five years.
Dr Mary Bousted, joint general secretary of the NEU, said: “Pupils are experiencing the inevitable result of several Government policies which have conspired to put a squeeze on schools.
"The real-terms funding crisis has had catastrophic effects, including a direct impact on class size. Today’s analysis will ring true for every parent who has witnessed their school cutting teaching assistant posts, reducing subject choice, or organising fundraiser events and begging letters.
"This is sadly all too common and a growing issue.
“In addition, teacher recruitment continues to lag behind the rise in pupil numbers, especially in secondary, with not enough done to attract subject specialists to the profession.
"Government targets are missed year upon year. A continued depression in teacher pay combined with high levels of workload means the Government has been vastly more effective at driving people out of teaching than in retaining them.
“Parents are no fools. They can see with their own eyes the impact of funding pressures on their children’s education, and the reduction in individual contact time that their child has with their teachers.
“Voters will scrutinise manifestos closely, and it would be foolish of any party to underrate the impact of education pledges, not to mention legacy, on the result. In this election the public knows that to value education, they must vote for education.”
The NEU surveyed its members on issues that they thought should be priorities for the next Government in order to improve the standard of pupils' education.
It found that 'reducing class size' was the top priority for 39 per cent of secondary staff and 21 per cent of primary staff.