Well, that might work, I haven't tried that kind of strategy yet. But a couple of points: this is a good strategy for dense cities especially because an elementary school in the center of a high-density residential block and full funding might not have enough space for all the students even at 50% bus funding. So, it is better to put the schools closer together.
One thing however, how large a city have you tested this with? I mean, you are saying that for 20k people, one would normally have 10 elementary schools? ! I have a 45K city (my biggest so far), and it has three elementary schools, one high school, and one library, and the education overlay shows green blocks all around. I have no idea what you would do with ten schools, not to speak of thirty in such a city.