Eureka math is a free math curriculum. Many schools use it, but anyone can download the teacher guides and worksheets free just by making an account. You can get to it at greatminds.org and there are videos and supplemental content you can use from embarc.online

I liked this program when I taught using it in the elementary classroom setting, and I now use it for my 6 year old's math instruction. It teaches the concepts (the why) behind the math. The idea is that if students understand why the math works, they can reason (critical thinking) out answers and understand if their answers make sense rather than just memorizing formulas.

One problem I saw in the public school system where Eureka math was used was when the teachers didn't really understand the math themselves and didn't teach the concepts correctly which caused confusion among the students, especially when it gets to the fourth and fifth grade levels where they are doing operations with fractions. If you are struggling with understanding a concept, watching the videos on embarc.online is helpful!

Hope this helps someone!