Here's how it works in my school: If he enters my class from someone else's, he's still seen the material. He can take the quiz and he'll do fine. I'm very fortunate that I work in a school that shares my own personal educational philosophy.
If he's been hospitalized and missed those days, I can certainly understand his absence. But he's still 2 days behind in the notes, and he'll have to make up the quiz one day after school when he can get the chance.
So if a kid goes to India or Arizona to visit Grandma and doesn't return until a month after school starts, are you suggesting that he not be responsible for the material he missed? How about if the trip lasts only 2 weeks? One week? Two days? Exactly when can I start to hold him responsible for the material all his classmates have learned... material that will be necessary later in the year, that will be on the trimester exam, the final exam, and that next year's teacher will assume he's learned?? Where in the extrapolation can we say "NOW school has started?" If "officially school starts the first day they are there" then are you suggesting that a kid who spends the first month of school in the park smoking pot is not responsible for the material being taught because he was smart enough not to come to school that first day??? Is it more OK if he's home with mom smoking pot and she writes a note saying he's sick? Exactly how much time am I supposed to be wasting with those kids who are in school from the start while we wait for others to get in??
Yes, I'm pushing it to ridiculous lengths. But my point is that there's a clear way to decide when the kids are responsible for the material being taught: the first day of school.
As I said, I understand that there are extraordinary circumstances that require kids to be out when they're not sick. But know that in my class, and in lots and lots of classes throughout the country, teachers will be teaching. We'll be doing the job we were hired to do, teaching any kids who show up.