In California, once a student attends school, regular attendance is required.   This includes TK and Kindergarten.  
Too many absences can cause children to fall behind in school.
Missing 10% (or about 18 days) can make it harder to learn to read and be successful in school.
Students who are chronically absent in kindergarten are less likely to read by 3rd grade. 
Students can still fall behind if they miss just a day or two days every few weeks.
Being late to school may lead to poor attendance.
Absences can affect the whole classroom if the teacher has to slow down learning to help children catch up.
 
What Parents can do:
Set a regular bedtime and morning routine.
Lay out clothes and pack backpacks the night before.
Find out what day school starts and make sure your child has the required shots.
Introduce your child to teachers and classmates before school starts to help them transition.
Don’t let your child stay home unless they are truly sick. Keep in mind complaints of a stomach ache or headache can be a sign of anxiety and not a reason to stay home.
If your child seems anxious about going to school, talk to teachers, school counselors, or other parents for advice on how to make them feel comfortable and excited about learning.
Develop back-up plans for getting to school if something comes up. Call on a family member, a neighbor, or another parent.
Avoid medical appointments and extended trips when school is in session.

 

Sources:
APS Attendance Supports
Attendance WorksExternal link 
Help Your Child Succeed Flyer (PDF) External link
Attendance in the Early Grades: Why it Matters for Reading (PDF)External link