But for Elementary level, there has to be something the parents can reference so they can help with homework.
It's a nice idea & sometimes it's helpful, but . . .
One of my biggest learning-curve moments as a first year teacher was a math lesson on skip-counting. Per the textbook, it was a one-day lesson on how to count by ones, twos, threes, fives, tens, twenty-fives, etc.
Took my third graders a week--
a week--to finish that stupid assignment, and all they achieved was the sense that they had no idea how to skip count.
The following year, I redesigned the lesson. (It's a good skill for 8-year-olds to know). We did about 8 different lessons & spent 8 days learning all the different patterns. How to look at the tens place when counting by tens. How the ones place alternated between 5 & 0 when counting by 5s, etc. Ultimately culminating in how to count up with your fingers for complex patterns like counting by 7s. The kids totally got it. They learned how to skip count, and they were confident.
Since then, I always rewrote math textbooks. I used a lot of the same problems, but I rewrote them onto worksheets that saved us 50% of the time because kids didn't have to copy the problems & then mess up because they had copied them wrong. (Thereby, we completed twice as many lessons & learned twice as many math skills during a year). I removed problems that were above students' developmental level. I made certain there weren't any trick questions that hadn't been explained in the lesson. I cut out a lot of excess busy work. I made sure students had enough practice time on each skill before throwing in something new. I wrote problems large enough so that students wouldn't make dumb, frustrating mistakes because there wasn't enough space. I wrote problems onto graph paper so numbers were lined up for carrying & borrowing correctly, etc. I designed full lessons on story problems so that students could learn how to solve them step-by-step.
This did sometimes make it harder for parents trying to help with homework. I always explained to parents that if they ran into this problem, they could write me a note & I would find a way to give their child extra help with the assignment. On average, only one or two students per class ever had parents that actually helped with homework of any kind. Over a number of years, I maybe received two notes from parents asking for their child to have help on a particular math assignment.
Rewriting a textbook takes a great deal of time; and, no, I did not have enough time to write or type out detailed directions for parents on worksheets for 9 months of the school year. But it was totally worth rewriting the lessons because my kids learned the math & had the confidence that they could do math.
Having said all that, the Engage NY curriculum that a lot of schools used here for @5 years because it was free & just printed off via an online program was totally detestable. Schools used it because it was free & the company had an oar in creating new state tests (Um, conflict-of-interest, hello?). And because it was free, many school districts overrode traditional teacher-led textbook committees in order to adopt the curriculum. It was a nightmare, and I think every local district has finally chucked it out the window after about 5 years of frustrating students, teachers, and parents.
Generally speaking, I think it is best to think of textbooks and online curriculum both as resources.