Here in Corona/Norco (about 30 mins. from DLR) many of our schools are year round. Those that aren't have summer break from Sat., June 13th and back to school on Sept. 2nd. Christmas Break is Sat., Dec. 20th and back to School and Jan. 5th.
But for those that are year round schools, 25% of our kids are off at any one time. Jan-Dec.
HTH.
And yes, other states can have a huge effect on DLR. Utah, Nevada, and Arizona. Even Northern Califoria effects it. In the beginning of Jan. when most local schools were back in session (my DD9 was off track) the parks were still pretty crowded. I spoke to several guests who were from up north and they said they got 3 weeks off which accounted for a lot of the extra people at DLR the week of Jan. 5th.