In Wisconsin, you do not need a special license to operate an ATV. However, all ATV operators who are at least 12 years-old and who were born on or after Jan. 1, 1988 must have a safety certificate in their possession when riding. To obtain a certificate you must complete an ATV safety certification course. Do so by getting a DNR customer number from the Go Wild website. Then visit one of the state's two approved vendors to register for the course.
Check out these Altoona, WI ATV/OHV resources:
