Not while in school, other than national holidays.
When you go into practice, it depends on WHERE you practice OR if you start your own. If you're good enough, you can set your own hours....if you work elsewhere, there are always going to be certain restrictions, but that depends on where you practice at...some have a rotating schedule (one or two peds will work "this" weekend, another 1 or 2 will work "next" weekend, etc.)...some demand weekends (though much shortened hours)...some always have weekends off.
When you get to that stage in your career, look for a practice that has more flexible hours. You'll most likely HAVE to work in a large practice before establishing your own.