My boys had a family tradition of going to the first day of the state fair with the grandmother and distant cousins (the grandfather's first cousin, his wife and their granddaughter). Allowing them to miss school depended on what grade they were in and how they were doing in their classes. Sometimes they missed the whole day, sometimes only a half day, sometimes they had to wait until school was out.
Education IS important, however, look at the time of the year. Kids aren't really learning anything right now. They are already in vacation mode. I would suggest allowing the child to go, however later on have a discussion with the father about the importance of school and that you just want both of you to be on the same page because if you take the child out of school for 11 days "because you can" and he does the same, then the child has missed 22 days and must repeat the grade.