There's an important point lurking in the 74's ballot article

You may have seen this article about Massachusett's ballot question on the charter cap making the rounds yesterday. Let's start by pointing out that this is where this article is coming from and these are not friends of public education.
That said, it's worth reading the article, which seems to be struggling to be fair, even as it can't resist making snide remarks about teachers' unions or districts thinking they are owned money. The bit about how "good" Massachusetts districts have it on charter reimbursements compared to the rest of the country is particularly rich.
I want to call attention, however, to their analysis--which could of course be wrong--of where the decision is going to fall on this:

Ironically, the fate of the referendum will probably come down to a unique set of swing voters: the suburban centers along the I-495 ring outside Boston that have no dog in this fight. Their schools are unaffected by charters. To put the question bluntly: Will the well-off white residents of Wellesley, Lexington, Newton, and Hopkinton vote to open up more charter school seats for low-income black and brown students from Roxbury, Dorchester, East Boston, and Mattapan?

First, it's really important to note that the middle sentence--"Their schools are unaffected by charters."--is completely inaccurate. For an easy visual, you can use the MTA's map, or, if you don't trust that, you can use what the MTA did, which is the Department of Elementary and Secondary Education's information (that's to the overall page; you'll need to download spreadsheets for more). Yes, suburban schools are absolutely losing funding, and seeing educational inequities, as a result of charter schools. Ask the 495 suburbs about AAMS or the 128 districts about Mystic Valley, for example.

Second, any district that has students going to a charter school loses out when there is expansion of charters. The reason for this is simple: the number of charter seats continues to go up; the amount of funding in charter reimbursement does not. (That's why, incidentally, this was in the Senate's RISE Act.) You have the same pie being cut into more pieces; each piece is smaller. None is fully funded.

Thus if the above is true, it's crucial that parents in every public school district realize the cost to their own district if the cap is lifted.