It's likely most of the objections will be over sex ed and evolution, but the law itself was inspired by a parent's objection to the book Nickle and Dimed by Barbara Ehrenreich (a worthwhile examination of minimum wage America). Most parents will not go to the trouble of objecting to phonics instruction or double digit subtraction, or the method by which either is taught, but it is theoretically possible. We could, however, see parents say things like multiculturalism is overused, the holocaust was overstated, or the civil rights movement was a mistake.
While schools shouldn't be platforms for teachers to share their political views, they also can't constantly answer to the whims of parents. Teachers already differentiate their instruction toward different levels, IEPs, 504s, and other accommodations. Differentiation based on parents' political leanings is not what public schools are designed to accomplish.