First, all student passwords have been reset to uppercase S lowercase t and the student's 6 digit birthdate. An example would be a birthday of February 17th, 2003 would be St021703.
In some cases, it seems that students need to have a network connection before logging into the computer. Tell them to click on the Wi-Fi icon before logging in, connect to their home Wi-Fi network, or the T-Mobile LTE network, then try logging in.
If that still doesn't work or they are using their own device, have them call the school to get their password unlocked. Any teacher or Library Clerk can unlock an account.