When Year 7 students work on addition and subtraction, they often make some mistakes that can confuse them. Here are a few common ones I've noticed:

1. Not Aligning Numbers Correctly

One big issue is not lining up the numbers right, especially when they have different amounts of digits. For example, if a student is adding $345 + 67$, they might not put the numbers in the correct columns for units, tens, and hundreds. This can easily lead to wrong answers.

2. Problems with Carrying and Borrowing

Students can also have trouble when they need to carry over a number in addition or borrow in subtraction. For instance, when adding $58 + 27$, if a student forgets to carry the $1$ from $15$, they will get the wrong answer. The same goes for subtraction—if they forget to borrow from the next column, it can cause big mistakes.

3. Confusion with Negative Numbers

Negative numbers can be tricky. Sometimes, students forget that when they take away a bigger number from a smaller one, the answer is negative. For instance, $5 - 8 = -3$ can be misunderstood, leading to errors.

4. Mixing Up the Order of Operations

Some students get confused about the order in which to do calculations, especially when there’s more than one step. For example, in a problem like $8 + 2 - 3$, if they do the addition before the subtraction, it can completely change the answer.

5. Making Rounding Mistakes

When dealing with larger numbers, students sometimes round numbers the wrong way, thinking it will make their math easier. While it's good to estimate, they shouldn't just guess. It’s important to be as accurate as possible unless they are told to estimate!

By knowing these common mistakes, students can get better at addition and subtraction. Practice will make these math skills become easier over time!