In Illinois, as mentioned above, you cannot compete club and high school sports at the exact same time (this is true for all sports, not just gymnastics). However, the winter season for high school sports (including gymnastics) runs from approximately early November to early February. You can find the exact dates and more information on the IHSA website (they have a 5-year gymnastics season calendar posted). So it is technically possible to do both. A gymnast would have to take a break from club gymnastics during the high school season, and then back to club right after. In addition, because the "last day" to qualify for Illinois USAG state meets is usually in early March (depending on level), there is typically time to compete at least one or two club meets, qualify for state, and then possibly on to regionals, etc. However, this only works IF your club allows its gymnasts to do both. It's my understanding that many do not.