I grew up before the daycare era. But I had two parents with professional jobs at a time when this was uncommon. There were times when I was disruptive in class. That these things are connected is entirely believable.
I think your point is well-taken. I was raised in a home with a mother who stayed home. I was a little disruptive in class (class clown type) but otherwise a good kid, as I've been told. My kids (boy/girl twins, now 15 years old) spent part-time in day care as my wife worked a 20 hour week as a pharmacist in an HMO. Neither of them is disruptive, and both have always been good students (my son is a very able student, while my daughter, while not with quite as much horse-power, has a very good work ethic).
I think the distinction is parental involvement in the child's life. Those who have to, or choose to, put their kids in day care often (not always, of course) find it difficult (or too much of a bother) to involve themselves in what is going on in their child's lives. That, I think, is the decisive factor, not the mere fact that they are in day care. Another factor is the kind of day care setting the child is placed in.
Kids can be shown what is proper behavior in various settings. One good place to learn this is Sunday School. While the rules are usually a little more relaxed there, the atmosphere is one of caring and nurture. And it doesn't last that long, so the child can become acclimated to what is expected. Couple that with learning to be quiet and still in church, and the likelihood of such a child being disruptive in school is greatly reduced.
If a child gets the attention he/she needs from home and elsewhere, he/she won't have to seek it by disruptive behavior in school.
Just my humble opinion.