Math is taught far too slowly in school. Kids go over fundamental arithmetic repeatedly, and kids typically don't even look into any algebra or geometry until the 8th or 9th grade. I remember going over PEMDAS for multiple years. PEMDAS would've began to make much more sense had I been introduced to algebra the same year. This would be equivalent to going over Ohm's law for years before even looking at a single electronic circuit. At least half of 4th graders have the mental capacity to understand basic algebra. The concept of plugging in for x in algebraic functions is not that difficult to grasp.

One of the first things I'd do is stop the practice of taking points off of asignments when students don't show their work. It makes sense for algebra and calculus, since you want to make sure your students conceptually understand the math, but not for fundamental arithmetic that can very easily be done mentally. This is why I really don't like common core. The biggest part of common core is grading kids for based on the work they show rather than the answers they give for common arithmetic equations that most adults can do mentally without much difficulty.

Growing up, I distincly remember learning multiplication a full year before I was supposed to. A girl who was one or two grade levels above mine was working on multiplication problems in the lunch room, and she was kind enough to explain the process to me.