Younger children are more likely to not be sufficiently physiologically developed to handle certain arithmetic operations. This has absolutely nothing to do with intelligence. It is simply a normal part of a child's development that you should be aware of. Some 7 or 8 year olds will struggle greatly with certain concepts.
Use the Equations Worksheet Generator to create a limitless supply of linear equations for solving. Alternatively, select from the list of pre-made worksheets below.
Simple Linear Equations
The worksheets below provide a gradual introduction that can help students
learn how to solve equations that include letters. e.g. x + 4 = 7. They allow
space for students to write the algebraic steps required to get the correct
answer. The bottom two on this list are aimed at students who struggle with memorizing multiplication facts.