It's important to remember that each child, even though diagnosed with ASD, is different. As the teacher, you need to figure out what motivates and interests them. I have several friends that all have children with Autism and there are not two that are the same. Their interests and quirks vary widely. My son LOVES girls and legos and drawing. He tries very hard but has difficulties grasping some subjects and then gets frustrated easily. For him we try to work off his drive to succeed. He has a chart with common words like: Jesus, Heavenly Father, love, baptism, family, church, etc. When he hears one of the words on his chart he puts an X by it and after church we count up the X's. For every 10, he gets a bag of treats. The bags could be skittles, goldfish, crayons, etc.
Good luck and get creative with your calling!