We are not in the American school system so I can't speak for the dates of their spring breaks, but we've taken two trips in March/early April.
The first one we were there at the very end of March, right after, apparently, the great majority of schools had spring break. It was awesome. You could fire a canon down the streets. I took several different pictures at different times of day where there were clear views down the streets.
A friend of mine went a week before us. It was wall-to-wall people. Her experience was so different from ours that she often jokes we never went to the same place. I'd talk about things that she never got to experience. They basically went and stood in line for rides for hours on end whereas we had the entire
Disneyland experience.
Our second trip was roughly the same time only that year Easter weekend fell at the end of our week. It was night and day in terms of crowds. We heard that the park attendance levels were at all-time record highs. It was packed, to say the least. There were rides that we literally walked on the last time that we stood in line for for 45 minutes to an hour. It was a very different experience for us.
I don't know if that gives you any ideas or not. I was told afterwards that the days leading up to Easter are ridiculous. (I didn't even notice Easter on the calendar when I originally booked it. My mistake.)
If our trips had been switched and our second experience had been our first, I don't know if we would have gone back the second time. The first time was downright idyllic! It was like they opened the park just for us, LOL! (Not really, but in our minds it was close enough.) The second time I actually encounter cranky CM's . . . something I thought was a myth. LOL! Totally understandable though, considering what they were being put through that week.
HTH a little!!