My job is full-time, why am I not getting benefits?

I work as an autism support aide in a school. Most people who work at the school and who work full time get good benefits. But for some reason, even though my position is full time I don't qualify for benefits. Neither do any of the other aides I am working with.

Can anyone explain why this would be the case? Is it legal to not offer benefits to full-time employees?

usa jobs
usa jobs resume
usa hotel jobs
usajobs
usa jobs federal government
usa job in ksa
usa jobs
usa jobs login
usa jobs gov
usajobs.gov
www.usajobs.gov
usajobs.com
usajobs
usajobs.gov official