Classrooms are too small physically to fit many more children along with the required computers and any inclusion adaptive equipment such as wheelchairs or other special chairs. There would be a decrease of support for schools by parents.
Class size is cited as the most important educational factor to most parents.
Increase class size in Junior High and High School Class size in the upper levels is a less meaningful indicator. At the Junior High School, teaming places 110-120 students with 5 teachers. At the high school different classes have vastly different enrollments. A lecture class can be fine with 30 students, but a remedial math should have far fewer. Besides the effect on the students, the effect on the teachers needs to be considered, when neighboring towns require teachers to teach fewer classes and fewer students, often for more money.