If your site is using a client code or school code, everyone at your organization must use the school code when logging in.
However, you can bookmark the school code in the URL to have its value pre-populated in the school code field. This is useful to do in labs where students are repeatedly logging in, especially for younger students.
See this example below. Go to Let's Go Learn's login page and then add a slash and your school code. For example, if your code is "xusd," you would bookmark this URL: https://frontend.letsgolearn.com/login/xusd