One tool I like to use to communicate with students and parents is Remind101.com. With Remind101 you can easily send a text message or email message to a class of students or to all of your students and parents. I especially like that I can set the time that the message will get set. Often I will set it to send the message out at 2:10pm because our last period ends at 2:15pm and my students will get the reminder just before they reach their lockers to go home.
My advice.. make up a separate class for each class period that you meet with. This way you can send a text and/or email message to every student in one class or every student in all classes.