If you have a teacher account and do not see the +Add Students button on the student roster page, this may indicate that student rostering is locked to the admin level for your school and/or district.
When students are locked, only district and school admins can create students, delete students, or modify student identities and login credentials. Once the admins have added students, teachers are able to modify reading levels and settings, assign reading content, and record assessment scores and progress monitoring data.
Please contact your school or district admin with questions. For help on where to find your account admins, see Where Can I Find the Admins on My Account?