Strictly speaking, your example is not "quantitative change causes qualitative change". He can only say that primary school students have learned two different methods of mathematical operation.

This change of "quantitative change leads to qualitative change" must be logical and natural. For example, if you teach a child 10 years of addition and subtraction instead of multiplication and division, do you think he will realize the multiplication and division by himself? Obviously not, so it's not like this.

For example:

You feel hungry after eating one cake, and full after eating six cakes. This has changed, which means you have changed from hungry to full.

You only have 100 yuan, so you can't live a good life. Accumulate slowly, work hard and get rich.