It depends. Copyright law in the U.S. allows for Teacher-Authors to own the rights to the original work they create as long as that work is created outside the scope of their employment with their school.
To ensure that you own the content that you’re uploading to TpT, it’s critical that you check your own school’s policies around copyright ownership. School boards will often publish policies around copyright ownership which define the bounds for creating and owning resources. For example, schools will typically claim ownership in cases where teachers use school time, resources, or funds to create their resources.
If you have specific questions about your policy or the law, we strongly recommend working with an attorney who specializes in intellectual property law.