* The students' needs: A classroom of 20 typically developing students might not require a paraprofessional, while a classroom of 10 students with significant disabilities might require several. The severity and type of disabilities significantly impact the need for support staff.
* The grade level: Younger students often require more individual attention.
* The school district's policies: Each district has its own student-to-staff ratios and guidelines for assigning paraprofessionals. Some districts may have stricter requirements than others.
* State regulations: State laws and regulations may also mandate specific student-to-staff ratios, particularly for students with Individualized Education Programs (IEPs).
* The teacher's experience and skills: An experienced teacher may be able to manage a larger class effectively than a less experienced teacher.
In short, it's impossible to give a numerical answer without knowing the specific context of the classroom and the applicable regulations. You need to consult the school district's policies and the relevant state regulations to determine the appropriate student-to-staff ratio.