If the parish uses a hymnal, just use that.

One of the goals of the school Mass absolutely should be continuity with the weekend Masses. You can supplement it if you'd like (for example, we taught the kids the Missa de Angelis Kyrie, which is not in Breaking Bread), but the consistency and continuity is quite helpful. Before I arrived at my current post (a parish with a school, where I nosed my way into the school Mass), the school used (sigh) Rise Up and Sing, and when I arrived the principal and I agreed it was time to move on from those. So we use the Breaking Bread hymnals in the pews, and it's worked well.

If the parish doesn't use a hymnal, I would stick with worship aids. Kids are very, very rough on books, but the kid-aged hymnals (mostly if not all in paperback) will fall apart quickly and the regular hymnals are too expensive for most school budgets. (The annual replacement of Breaking Bread is an advantage here, as it's a parish cost and the kids don't have enough time to damage them.)

I would be happy to send you the resource that I have put together for my school. (Pre-k through 12.)

In short, we use the graduale simplex and a selection of hymn suite with hymns to mirror the GS within Mass.

I'm currently refining a bit more for this year, but I'm happy to share the document for your own use of it would be of help! (Or even just as an idea booklet).

I wouldn’t assume that there is a parish or if there is that they’re necessarily in the same building,

Indeed. I can send that booklet along sometime today or tomorrow. I'm currently in the process of revising it ... Let me send the old version (cleaned up of parish identifiers) and then I'll send along the 2nd edition.

Thank you everyone for suggestions, and please feel free to continue discussing this topic here and sharing resources.

It might be that in the long term printing a localized hymnal/missal/song book might be a possibility, someday... but the trouble is at least some of the favorites of the students include some contemporary works that I think would prove troublesome to license for a local publication.

In the nearer term I think I will need to put in some work on a sort of core repertoire, a minimum essential list of what the students should learn to sing for liturgy and paraliturgical devotions. The ordinary and simple dialogues of the mass in English and Latin would I think be easy to justify as part of such a list. Given our growing emphasis on Hispanic ministries and such we could perhaps justify the Spanish, too, at least for the older students. After that it becomes a bit harder to really justify individual selections. I could take Paul VI as an authority for recommending the entire Jubilate Deo contents (probably the shorter original rather than the 1987 expanded), but beyond that no one with much authority (juridical or moral) has put out such a minimum core repertoire in English (there was talk of such once at the USCCB, but the project either was cancelled entirely, or is on permanent back burner at least).

I think such a minimum repertoire could be approached from two directions:
Essential texts and essential melodies.

I think here the temptation, like with the expansion of the Jubilate Deo chant collection itself, is to always keep adding more stuff because it is good stuff, but a key criteria for any sort of core shared repertoire or minimum essential list is being a bare minimum and tightly curated. I am open to suggestions or recommendations on this front.