In kindergarten through third grade, students can solve almost all of their problems by memorizing their facts or drawing quick pictures. However, these same strategies are less effective when students get to fourth grade and have to solve multi-digit problems.
Consider a third-grade student who is taught to use skip counting by 6 or memorization to solve 48/6.
Now imagine this same student in fourth grade. What strategy might they use to solve 486/6?
You are going to need strong number sense to solve the above problem.
While skip counting and memorization might get students through third grade successfully, students will need number sense (algebraic thinking) to solve problems with multi-digit numbers efficiently.
They will need a deep understanding of place value and the base ten number system before advancing to more sophisticated strategies.
They will need to practice composing and decomposing numbers every day.
If kinder through third-grade students are not highly skilled in all of the above, fourth grade is going to be a real challenge. Memorization, skip counting, and circles and sticks will only get them so far.
I wonder might the lack of number sense, composing and decomposing, and the use of place value as a strategy be the cause of fourth-grade scores hitting a wall and going down.